Test method of ion activity in solution, preparation method of working curve of solution, test device of working curve and test method of lithium ion activity

Abstract

The invention relates to the technical field of analytical chemistry, and relates to a method for testing ion activity in a solution, the method comprises the following steps: preparing a reference solution and a working solution, the reference solution and the working solution comprise a solvent, a reference substance with redox activity and a salt, and the cation element of the salt comprises a metal element A; preparing a working electrode and a counter electrode, wherein the material of the counter electrode comprises metal A; performing cyclic voltammetry test on the working electrode and the counter electrode in the working solution to obtain working potential E1; performing cyclic voltammetry test on the working electrode and the counter electrode in the reference solution to obtain a reference potential E2; and calculating the activity a1 and a2 of the metal ions of the working solution A according to an equation, wherein the activity a1 and a2 are the activity of the metal ions of the reference solution A, R is a gas constant, T is temperature, z is the charge number in the battery reaction, and F is a Faraday constant. According to the test system, the working electrode and the counter electrode are tested in the single-phase solution, so that the test accuracy is improved.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry, and in particular to a method for testing the activity of ions in solution, a method for preparing a working curve thereon, a testing apparatus therefor, and a method for testing lithium ion activity. Background Technology

[0002] In chemistry, ion activity refers to the effective concentration of ions in an electrolyte solution, reflecting the actual behavior of ions in the solution. Ion activity is the effective concentration of ions participating in chemical reactions in solution, which differs from the actual concentration of ions. It takes into account the interactions between ions and the influence of the solvent.

[0003] The activity test of electrolyte in ion-ion batteries is one of the key parameters for evaluating their performance. The activity of the electrolyte directly affects the ion conduction performance, thus affecting the overall performance and lifespan of the battery. Summary of the Invention

[0004] The main objective of this invention is to provide a method for testing the activity of ions in solution, aiming to improve the accuracy of testing the activity of ions in solution.

[0005] To achieve the above objectives, this invention proposes a method for testing the activity of ions in solution, characterized by comprising:

[0006] Prepare a reference solution and a working solution, wherein the reference solution and the working solution include a solvent, a redox-active reference substance and a salt, wherein the cation element of the salt includes an A metal element;

[0007] Prepare a working electrode and a counter electrode, wherein the material of the counter electrode includes metal A;

[0008] The working electrode and the counter electrode are subjected to cyclic voltammetry tests in the working solution to obtain the working potential E1.

[0009] The working electrode and the counter electrode were subjected to cyclic voltammetry tests in the reference solution to obtain the reference potential E2.

[0010] According to the equation Calculate the activity a1 of metal ions A in the working solution, where a2 represents the activity of metal ions A in the reference solution, R is the gas constant, T is the temperature, z is the charge number in the battery reaction, and F is the Faraday constant.

[0011] The following steps can be used to test the ion activity in the solution: Prepare a reference solution and a working solution, which include a solvent, a redox-active reference substance, and a salt. The cation element of the salt includes metal A. The activity a1 of metal A ions in the reference solution is known. Prepare a working electrode and a counter electrode, the counter electrode being made of metal A. Perform cyclic voltammetry on the working electrode and counter electrode in the working solution to obtain the working potential E1. Perform cyclic voltammetry on the working electrode and counter electrode in the reference solution to obtain the reference potential E2. That is, during the cyclic voltammetry test, the redox potential of the redox-active reference substance is measured using the working electrode. This potential reflects the potential difference of the counter electrode in the reference solution and the working solution. Based on this potential difference, the activity a1 of metal A ions in the reference solution is determined according to the equation... Calculate the activity a1 of metal ions A in the working solution, where a2 represents the activity of metal ions A in the reference solution, R is the gas constant, T is the temperature, z is the charge number in the cell reaction, and F is the Faraday constant.

[0012] That is, this application adds a reference substance with redox activity to solutions with different salt concentrations, and tests the redox potential of the reference substance with redox activity through the working electrode. The redox potential of the reference substance reflects the potential difference of the counter electrode in solutions of different concentrations. By combining the potential difference with the above equation, the difference in activity (activity of metal ions) of salts with different concentrations (the cation of the salt is metal element A) in the solution can be obtained. Given the known activity a2 of metal ions in the reference solution, the activity a1 of metal ions in the working solution can be calculated.

[0013] Furthermore, during the testing of the working potential E1 and the reference potential E2, both the working electrode and the counter electrode are placed in the same solution. That is, the working electrode and the counter electrode are tested in a single-phase solution, which eliminates common interference factors in multiphase systems, avoids potential measurement errors and diffusion effects caused by electrolytes of different concentrations in the same testing device, and improves the accuracy of the test.

[0014] Optionally, the oxidation potential of the reference substance is lower than that of the working electrode, the counter electrode, and the solvent;

[0015] The reduction potential of the reference substance is higher than that of the working electrode, the counter electrode, and the solvent.

[0016] Understandably, to avoid interference, the electrochemical window of the reference material needs to cover the electrochemical reaction potential range of the working electrode, counter electrode, and solvent. The oxidation potential of the reference material should be lower than the oxidation potentials of the working electrode, counter electrode, and solvent. This ensures that the reference material is oxidized before the working electrode, counter electrode, and solvent, thus serving as a reference; that is, the oxidation potential of the reference material is measured by cyclic voltammetry. The reduction potential of the reference material should be higher than the reduction potentials of the working electrode, counter electrode, and solvent. This ensures that the reference material is reduced before the reduction of the working electrode, counter electrode, and solvent, thus serving as an internal control; that is, the reduction potential of the reference material is measured by cyclic voltammetry.

[0017] Optionally, the oxidation potential of the reference material is at least 0.1V lower than the oxidation potentials of the working electrode, the counter electrode, and the solvent;

[0018] The reduction potential of the reference substance is at least 0.1V higher than the reduction potential of the working electrode, the counter electrode, and the solvent.

[0019] Typically, the oxidation potential of the reference material is required to be at least 0.1 V (100 mV) lower than the oxidation potentials of the working electrode, the counter electrode, and the solvent, and the reduction potential of the reference material is required to be at least 0.1 V (100 mV) higher than the reduction potentials of the working electrode, the counter electrode, and the solvent.

[0020] Optionally, at least one of the following conditions must be met:

[0021] Condition A: The redox potential of the reference material relative to the standard hydrogen electrode ranges from -3V to 1V;

[0022] Condition B: The standard electrode potential of metal A relative to the standard hydrogen electrode is -4V to 1V;

[0023] Condition C: The reference substance includes metal compounds and / or metal complexes;

[0024] Condition D: The metal element A includes any one of lithium, zinc, magnesium, and calcium.

[0025] In one embodiment, the redox potential of the reference material relative to the standard hydrogen electrode meets the above-mentioned range. This improves the accuracy of the test.

[0026] In one embodiment, the standard electrode potential of metal A relative to the standard hydrogen electrode satisfies the above-mentioned range. This improves the accuracy of the test.

[0027] In one embodiment, the reference material includes a metal compound and / or a metal complex. It is understood that a metal compound refers to a compound formed by a metal element and other non-metallic elements or compounds, and a metal complex refers to a compound formed by a metal central ion (or atom) and a ligand capable of donating lone pairs of electrons through coordinate bonds. The ligands are typically organic or inorganic molecules capable of forming coordinate bonds with the metal center. The reference material with redox activity can be a metal compound and / or a metal complex.

[0028] In one embodiment, metal element A includes any one of lithium, zinc, magnesium, and calcium. For example, when the ion activity to be tested is lithium ion activity, that is, when the cation of the salt to be tested is lithium, metal element A is lithium.

[0029] Optionally, the metal compound includes a metallocene compound;

[0030] And / or, the metal complex includes at least one of metalloporphyrin and metal pyridine.

[0031] It is understandable that metal compounds and metal complexes include the compounds mentioned above.

[0032] Optionally, the metallocene compound includes at least one of ferrocene, cobalt dicene, and nickel dicene;

[0033] And / or, the metalloporphyrin includes at least one of nickel(II)porphyrin, nickel(III)porphyrin, cobalt(II)porphyrin, cobalt(III)porphyrin, and tetracarboxyphenylporphyrin cobalt;

[0034] And / or, the metal pyridine includes a multidentate pyridine ligand complex.

[0035] Taking metallocene compounds as an example, metallocenes contain one transition metal atom and two cyclopentadiene ligands, forming a sandwich structure. Metallocene compounds exhibit good potential stability. Because the redox potential of the reference material is also relatively stable, the measured potential essentially reflects the potential difference of the counter electrode in solutions with varying salt concentrations. Among them, ferrocene, cobalt dicene, and nickel dicene possess large delocalization charges and good stability, showing less interference from solvents and salts in solution, thus improving the accuracy of the test.

[0036] Metalloporphyrins include at least one of nickel(II)porphyrin, nickel(III)porphyrin, cobalt(II)porphyrin, cobalt(III)porphyrin, and tetracarboxyphenylporphyrin cobalt. Metal pyridines include polydentate pyridine ligand complexes, which are a class of organic ligands containing two or more pyridine rings as coordination sites, and they can form stable coordination compounds with metal ions.

[0037] Optionally, the ferrocene includes at least one of butylferrocene, 1,1'-dimethylferrocene, tert-butylferrocene, and ferrocene decane;

[0038] And / or, the multidentate pyridine ligand includes ruthenium terpyridine (II).

[0039] Understandably, metallocene compounds have large delocalization charges. The higher the degree of charge delocalization and the greater the steric hindrance, the better their stability. Butylferrocene, 1,1'-dimethylferrocene, tert-butylferrocene, and ferrocene decane are compounds with even higher degrees of charge delocalization and greater steric hindrance. They have better solubility and stability in solution, which can reduce the interference of environmental factors on potential measurements, thereby providing a stable and reliable potential reference and improving the accuracy of measurements.

[0040] Multidentate pyridine ligands include ruthenium(II) terpyridine.

[0041] Optionally, at least one of the following conditions must be met:

[0042] Condition A: The concentration range of the reference substance is 1 mM to 100 mM;

[0043] Condition B: The concentration of the salt in the reference solution ranges from 0.1 mM to 100 mM, and the concentration of the salt in the reference solution is equal to the value of a2;

[0044] Condition C: The solvent includes aprotic solvents;

[0045] Condition D: The salt includes at least one of lithium salt, zinc salt, magnesium salt, and calcium salt;

[0046] Condition E: The working electrode includes any one of a Pt electrode, a glassy carbon electrode, and a carbon electrode. In one embodiment, the concentration range of the reference substance is 1 mM to 100 mM. It is understood that the concentration of the reference substance affects the accuracy of the test, and that the accuracy of the test can be improved by ensuring that the concentration of the reference substance meets the above range.

[0047] In one embodiment, the salt concentration in the reference solution ranges from 0.1 mM to 100 mM, and the salt concentration in the reference solution is equal to the value of a2. In this application, the reference solution is a solution with known activity. Typically, a lower concentration solution is chosen as the reference solution. Under low concentration conditions, the salt in the solution is approximately completely dissociated, and the activity is close to its concentration. Therefore, the activity of the salt in the low-concentration solution can be considered known. It is understood that different salts have different degrees of dissociation. In salt solutions with a high degree of dissociation, a concentration of 100 mM can be used as the reference solution, while in salt solutions with a low degree of dissociation, a concentration of 0.1 mM can be used as the reference solution.

[0048] In one embodiment, the solvent includes an aprotic solvent. An aprotic solvent is one that does not contain free protons (hydrogen ions H+). + Solvents that do not form hydrogen bonds by releasing protons when dissolving the solute. Generally, some metals react readily in protic solvents; to reduce interference from the reaction on the electrode, solvents include aprotic solvents.

[0049] In one embodiment, the salt includes at least one selected from lithium salt, zinc salt, magnesium salt, and calcium salt.

[0050] In one embodiment, the working electrode includes any one of a Pt electrode, a glassy carbon electrode, and a carbon electrode. It is understood that the working electrode itself does not react and is an inert electrode.

[0051] Optionally, at least one of the following conditions must be met:

[0052] Condition A: The aprotic solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether;

[0053] Condition B: The lithium salt anion includes PF6. - FSI - TFSI - At least one of them;

[0054] Condition C: The redox potential of the reference substance relative to the standard hydrogen electrode is within the redox window of the aprotic solvent relative to the standard hydrogen electrode.

[0055] In one embodiment, the aprotic solvent includes at least one selected from ethylene carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. For example, in one embodiment, it is necessary to test the lithium-ion activity of the electrolyte in a lithium-ion battery, and the solvent in the electrolyte includes ethylene carbonate and dimethyl carbonate.

[0056] In one embodiment, the lithium salt anion includes at least one of the above-mentioned, TFSI - It is a bis(trifluoromethanesulfonyl)imide, FSI - It is a bis(fluorosulfonyl)imide.

[0057] In one embodiment, the redox potential of the reference material relative to the standard hydrogen electrode is within the redox window of the aprotic solvent relative to the standard hydrogen electrode. By ensuring that the redox potential of the reference material is within the redox window of the aprotic solvent, unnecessary oxidation or reduction of the solvent can be avoided, thereby improving the efficiency and stability of the electrochemical system.

[0058] Optionally, the step of performing cyclic voltammetry tests on the working electrode and the counter electrode in the working solution to obtain the working potential E1 includes:

[0059] The working electrode and the counter electrode together with the working solution form a working electrolytic cell. A diaphragm is provided between the working electrode and the counter electrode to divide the working electrolytic cell into a working electrode chamber and a counter electrode chamber. The working solution in the working electrode chamber includes the reference substance.

[0060] The working electrode and the counter electrode are connected to an electrochemical workstation, and a working cyclic voltammetry curve is obtained on the electrochemical workstation. The working potential E1 is obtained from the working cyclic voltammetry curve.

[0061] In the process of forming the test system, the working electrode and the counter electrode are inserted into the working solution to form a working electrolytic cell. A diaphragm is placed in the working electrolytic cell between the working electrode and the counter electrode to divide the working electrolytic cell into a working electrode chamber and a counter electrode chamber. The working solution in the working electrode chamber includes a reference substance, while the counter electrode chamber does not contain a reference substance to reduce the interference of the reference substance on the counter electrode. The working electrode and the counter electrode are connected to an electrochemical workstation, and the working cyclic voltammetry curve is obtained on the electrochemical workstation. The working potential E1 is obtained from the working cyclic voltammetry curve.

[0062] In other words, a diaphragm is placed between the working electrode and the counter electrode. The diaphragm can reduce the influence of the reference substance in the solution on the counter electrode potential, reduce the risk of electrode contamination, improve the measurement stability and reliability of the electrolytic cell, and ensure the accuracy of potential measurement.

[0063] Optionally, the step of performing cyclic voltammetry tests on the working electrode and the counter electrode in the reference solution to obtain the reference potential E2 includes:

[0064] The working electrode and the counter electrode together with the reference solution form a reference electrolytic cell. A diaphragm is provided between the working electrode and the counter electrode to divide the reference electrolytic cell into a working electrode chamber and a counter electrode chamber. The reference solution in the working electrode chamber includes the reference substance.

[0065] The working electrode and the counter electrode are connected to an electrochemical workstation, and a reference cyclic voltammetry curve is obtained on the electrochemical workstation. The reference potential E2 is obtained from the reference cyclic voltammetry curve.

[0066] In other words, a diaphragm is placed between the working electrode and the counter electrode. The diaphragm can reduce the influence of the reference substance in the solution on the counter electrode potential, reduce the risk of electrode contamination, improve the measurement stability and reliability of the electrolytic cell, and ensure the accuracy of potential measurement.

[0067] Optionally, at least one of the following conditions must be met:

[0068] Condition A: The electrolytic cell is an H-type electrolytic cell;

[0069] Condition B: The material of the diaphragm includes at least one of porous polymer, ceramic, and glass fiber diaphragm.

[0070] In one embodiment, an H-type electrolytic cell design is employed, in which the working electrode and the counter electrode are placed in two separate chambers of the H-type electrolytic cell. The H-type electrolytic cell consists of a cathode chamber, an anode chamber, and an ion exchange membrane. This design allows two different chemical reactions to occur simultaneously in the separated chambers, while the ion exchange membrane allows ions to pass through to maintain charge balance. A reference substance is added to the solution on one side of the working electrode to reduce interference from the reference substance on the counter electrode.

[0071] In one embodiment, the diaphragm is made of at least one of the materials described above.

[0072] Optionally, at least one of the following conditions must be met:

[0073] Condition A: In the step of performing cyclic voltammetry tests on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the number of scan cycles of the cyclic voltammetry test is 3 to 100.

[0074] Condition B: In the step of performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1 ;

[0075] Condition C: In the step of performing cyclic voltammetry tests on the working electrode and the counter electrode in the reference solution to obtain the reference potential E2, the number of scan cycles of the cyclic voltammetry test is 3 to 100.

[0076] Condition D: In the step of performing cyclic voltammetry on the working electrode and the counter electrode in the reference solution to obtain the reference potential E2, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1 .

[0077] In one embodiment, in the step of performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the number of scans in the cyclic voltammetry test is from 3 to 100.

[0078] During cyclic voltammetry testing, the random error in a single measurement is averaged through multiple scans to further improve measurement accuracy.

[0079] In one embodiment, in the step of performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1 .

[0080] In cyclic voltammetry, the scan rate can affect the kinetics of the electrode reaction. A slower scan rate allows sufficient time for the reaction to reach equilibrium, while a rapid scan may keep the reaction in a non-equilibrium state. Considering the differences in reaction kinetics among different solution systems, an appropriate scan rate can be selected within the above range to provide flexible and rapid experimental conditions to meet the needs of different systems.

[0081] In one embodiment, in the step of performing a cyclic voltammetry test on the working electrode and the counter electrode in the reference solution to obtain a reference potential E2, the number of scans in the cyclic voltammetry test is from 3 to 100.

[0082] During cyclic voltammetry testing, the random error in a single measurement is averaged through multiple scans to further improve measurement accuracy.

[0083] In one embodiment, in the step of performing cyclic voltammetry on the working electrode and the counter electrode in the reference solution to obtain the reference potential E2, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1 .

[0084] Considering the differences in reaction kinetics among different solution systems, an appropriate scan rate can be selected within the above range to provide flexible and rapid experimental conditions to meet the needs of different systems.

[0085] Optionally, this application also provides a method for preparing a working curve of ion activity in solution, comprising:

[0086] Prepare the reference solution and working solutions of salts at different concentrations;

[0087] The activity of metal A ions in the working solution of each salt concentration is tested using a test method as described above for testing the activity of ions in solution.

[0088] Plot a working curve of the activity of the metal ion A versus the concentration of the salt.

[0089] A working curve is a tool used in analytical chemistry for quantitative determination. This application describes a method for preparing a reference solution and working solutions of salts at different concentrations; testing the activity of metal A ions in each concentration of working solution using the aforementioned testing method; and plotting a working curve of metal A ion activity versus salt concentration. By inputting the concentration of the salt in the corresponding solution into the working curve, the activity of metal A ions at that salt concentration can be obtained. It is understood that in the step of inputting the concentration of the salt in the corresponding solution into the working curve, the concentration of the salt refers to the concentration of a salt whose cation element is metal A. For example, when testing the activity of lithium ions in the working solution, the corresponding salt in the working solution is a lithium salt, and the concentration of the lithium salt is input into the working curve.

[0090] Optionally, in the step of testing the activity of metal ion A in the working solution of each salt concentration using the test method, the activity of metal ion A in the working solution of each salt concentration is tested at least twice, with an interval of 1 min to 30 min between each test, and the average value and standard deviation of the activity of metal ion A are calculated.

[0091] The standard deviation is the square root of the mean of the squares of the differences between each value in a set of values ​​and the mean. It reflects the degree of dispersion of the values ​​in the dataset relative to the mean.

[0092] By repeating the test multiple times, the average value and standard deviation of the activity are calculated. If a data point in a set of values ​​deviates significantly from the average value during the test, that data point can be discarded and the test repeated to reduce errors and improve the accuracy of the test. Furthermore, the time interval between each test is within the above range to reduce the impact of unbalanced and unstable solutions.

[0093] Optionally, this application also provides an apparatus for a method of testing ion activity in solution as described above, comprising:

[0094] An electrolytic cell containing a solution comprising a solvent, a redox-active reference substance, and a salt, wherein the cation element of the salt includes an A metal element.

[0095] A working electrode, wherein the working electrode is disposed in the electrolytic cell;

[0096] Counter electrode, the counter electrode is disposed in the electrolytic cell, and the material of the counter electrode includes the metal A;

[0097] An electrochemical workstation includes testing software, a working electrode interface, and a counter electrode interface. The working electrode interface is connected to the working electrode, and the counter electrode interface is connected to the counter electrode.

[0098] The above-mentioned device can be used to measure the ion activity in the test solution.

[0099] Optionally, this application also provides a method for testing the activity of lithium ions in a lithium-ion battery electrolyte, the method comprising the method for testing the activity of ions in solution as described above, wherein the salt is a lithium salt and the material of the counter electrode is lithium metal.

[0100] Testing the activity of lithium ions in lithium-ion battery electrolytes is one of the key parameters for evaluating their performance. The activity of lithium ions in the electrolyte directly affects ion conductivity, thus influencing the overall performance and lifespan of the battery. The method described above can accurately test the activity of lithium ions in lithium salts within the electrolyte, providing a reliable basis for evaluating electrolyte performance.

[0101] This application involves preparing a reference solution and a working solution, each containing a solvent, a redox-active reference substance, and a salt. The cation element of the salt includes metal A, and the activity a1 of the metal A ions in the reference solution is known. A working electrode and a counter electrode are prepared, the counter electrode being made of metal A. Cyclic voltammetry is performed on the working electrode and counter electrode in the working solution to obtain the working potential E1. Cyclic voltammetry is then performed on the working electrode and counter electrode in the reference solution to obtain the reference potential E2. In other words, during the cyclic voltammetry test, the redox potential of the redox-active reference substance is measured using the working electrode. This potential reflects the potential difference of the counter electrode between the reference solution and the working solution. Based on this potential difference, the equation is used to determine the potential difference. Calculate the activity a1 of metal ions A in the working solution, where a2 represents the activity of metal ions A in the reference solution, R is the gas constant, T is the temperature, z is the charge number in the cell reaction, and F is the Faraday constant.

[0102] That is, this application adds a reference substance with redox activity to solutions with different salt concentrations, and tests the redox potential of the reference substance with redox activity through the working electrode. The redox potential of the reference substance reflects the potential difference of the counter electrode in solutions of different concentrations. By combining the potential difference with the above equation, the difference in activity (activity of metal ions) of salts with different concentrations (the cation of the salt is metal element A) in the solution can be obtained. Given the activity a2 of the reference solution, the activity a1 of metal ions in the working solution can be calculated.

[0103] Furthermore, during the testing of the working potential E1 and the reference potential E2, both the working electrode and the counter electrode are placed in the same solution. That is, the working electrode and the counter electrode are tested in a single-phase solution, which eliminates common interference factors in multiphase systems, avoids potential measurement errors and diffusion effects caused by electrolytes of different concentrations in the same testing device, and improves the accuracy of the test. Attached Figure Description

[0104] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0105] Figure 1 This is a schematic flowchart of the method for testing the ion activity in solution according to this application;

[0106] Figure 2 This is a schematic diagram of the structure of the device for testing the activity of ions in solution provided in Embodiment 1 of this application;

[0107] Figure 3 This is a schematic diagram of the structure of the device for testing the activity of ions in solution provided in Embodiment 2 of this application;

[0108] Figure 4 This is a schematic diagram of the device for measuring ion activity in solution using a concentration cell, provided in Comparative Example 1 of this application.

[0109] Figure 5 These are the activity-concentration curves obtained from tests in Examples 1, 2, and Comparative Example 1 of this application.

[0110] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0111] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0112] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the method for testing ion activity in solution, the method for preparing the working curve, and the testing apparatus of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0113] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0114] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0115] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0116] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0117] The activity test of electrolyte in ion-ion batteries is one of the key parameters for evaluating their performance. The activity of the electrolyte directly affects the ion conduction performance, thus affecting the overall performance and lifespan of the battery.

[0118] The activity of the electrolyte can be calculated using the concentration cell potential combined with the Nernst equation. For example... Figure 4The diagram shows a schematic of a concentration cell device for measuring solution activity. In the concentration cell, the lithium metal electrode is placed in electrolytes of different concentrations. A 1 mM lithium salt electrolyte is selected as the reference solution. Under these conditions, the salt in the electrolyte is approximately completely dissociated, and its activity is close to its concentration. Therefore, the activity a1 (lithium ion activity) of the lithium salt in the reference electrolyte can be considered known. The potential difference (ΔV) of the concentration cell is measured using a voltmeter, and the activity a2 (lithium ion activity) of the lithium salt in the working electrolyte is calculated using the Nernst equation. The relationship between the electromotive force and the activity difference, after transformation of the Nernst equation, is as follows: Where ΔV is the measured potential difference, R is the gas constant (approximately 8.314 J / (mol·K)), T is the temperature (Kelvin), z is the charge number in the battery reaction, and F is the Faraday constant (approximately 96485 C / mol). By rearranging the Nernst equation, the expression for the activity a2 of the lithium salt in the working electrolyte can be obtained:

[0119] The aforementioned concentration cell structure has a multiphase interface, which can significantly affect the accuracy of the test.

[0120] To address the accuracy issues in testing caused by multiphase interfaces in concentration cell structures, such as... Figure 1 As shown, this application provides a method for testing the ion activity in solution, comprising: preparing a reference solution and a working solution, wherein the reference solution and the working solution include a solvent, a redox-active reference substance, and a salt, wherein the cation element of the salt includes a metal element A; preparing a working electrode and a counter electrode, wherein the material of the counter electrode includes a metal A; performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain a working potential E1; performing cyclic voltammetry on the working electrode and the counter electrode in the reference solution to obtain a reference potential E2; and applying the equation... Calculate the activity a1 of metal ions A in the working solution, where a2 represents the activity of metal ions A in the reference solution, R is the gas constant, T is the temperature, z is the charge number in the cell reaction, and F is the Faraday constant.

[0121] Activity is the effective concentration of a substance in a solution. It represents the deviation of a substance’s behavior in a real mixture from its behavior in an ideal mixture.

[0122] A reference solution includes a solvent, a redox-active reference substance, and a salt, wherein the activity of the salt (the activity of metal A ions) is known.

[0123] The working solution includes a solvent, a redox-active reference substance, and a salt. The concentration of the salt in the working solution is known, and its activity is the value to be measured.

[0124] A solution is a homogeneous and stable mixture of two or more substances. In this mixture, at least one substance is called the solvent, and the other one or more substances are called the solutes.

[0125] Solvents are the main components of solutions; they dissolve other substances to form solutions.

[0126] A redox-active reference material refers to a reference material that has redox activity. Redox activity refers to the ability of a substance to participate in electron transfer during a redox reaction. The redox potential of a redox-active reference material can be tested in an electrolytic cell using a working electrode.

[0127] Salts are a class of compounds composed of cations (positively charged) and anions (negatively charged).

[0128] The working electrode is where the main redox reaction occurs in the electrolytic cell. For example, in this scheme, the working electrode is used to test the redox potential of the reference substance.

[0129] The counter electrode, which is opposite the working electrode, completes the circuit and allows current to flow. The function of the counter electrode is to provide a source of electrons or receive electrons to maintain the electrolysis process.

[0130] In the step of performing cyclic voltammetry on the working electrode and counter electrode in the working solution to obtain the working potential E1, the working electrode and counter electrode are inserted into the working solution to form an electrolytic cell. The working electrode and counter electrode are connected to an electrochemical workstation. Cyclic voltammetry is used to test the redox potential of the reference substance using the working electrode. This is the working potential E1.

[0131] In the step of performing cyclic voltammetry on the working electrode and the counter electrode in a reference solution to obtain the reference potential E2, the working electrode and the counter electrode are inserted into the reference solution to form an electrolytic cell. The working electrode and the counter electrode are connected to an electrochemical workstation. Cyclic voltammetry is used to test the redox potential of the reference substance using the working electrode, which is the reference potential E2.

[0132] The following steps can be used to test the ion activity in the solution: Prepare a reference solution and a working solution, which include a solvent, a redox-active reference substance, and a salt. The cation element of the salt includes metal A. The activity a1 of the salt in the reference solution is known. Prepare a working electrode and a counter electrode, the counter electrode being made of metal A. Perform cyclic voltammetry on the working electrode and counter electrode in the working solution to obtain the working potential E1. Perform cyclic voltammetry on the working electrode and counter electrode in the reference solution to obtain the reference potential E2. That is, during the cyclic voltammetry test, the redox potential of the redox-active reference substance is measured using the working electrode. This potential reflects the potential difference of the counter electrode in the reference solution and the working solution. Based on this potential difference, the activity a1 of the salt in the reference solution is determined according to the equation... Calculate the activity of the salt in the working solution, a1 (activity of metal ion A), where a2 represents the activity of metal ion A in the reference solution, R is the gas constant, T is the temperature, z is the charge number in the cell reaction, and F is the Faraday constant.

[0133] That is, this application adds a redox-active reference substance to solutions with different salt concentrations, and tests the redox potential of the redox-active reference substance through the working electrode. The redox potential of the reference substance reflects the potential difference of the counter electrode in solutions of different concentrations. By combining the potential difference with the above equation, the difference in activity (activity of metal ions) of salts of different concentrations (the cation element of the salt is metal element A) in the solution can be obtained. Given the activity a2 of the reference solution, the activity a1 of the salt in the working solution can be calculated.

[0134] Furthermore, during the testing of the working potential E1 and the reference potential E2, both the working electrode and the counter electrode are placed in the same solution. That is, the working electrode and the counter electrode are tested in a single-phase solution, which eliminates common interference factors in multiphase systems, avoids potential measurement errors and diffusion effects caused by electrolytes of different concentrations in the same testing device, and improves the accuracy of the test.

[0135] It is understandable that the concentration cell structure faces issues such as the liquid junction potential at the multiphase interface, diffusion caused by the concentration difference, and measurement accuracy.

[0136] Specifically, taking electrolyte solutions as an example, regarding the liquid junction potential: the liquid junction potential refers to the potential difference at the interface of electrolytes of different concentrations due to differences in ion mobility. This difference introduces measurement errors, making the electrolyte activity calculated by the Nernst equation inaccurate. The accuracy of the liquid junction potential depends on the solution composition and ion types, and is usually difficult to control and predict precisely, and cannot be corrected by fixed parameters. Although salt bridges can reduce the influence of the liquid junction potential, the preparation of salt bridges in organic systems is difficult, has low maturity, and makes it difficult to conduct stable experiments.

[0137] Regarding diffusion caused by concentration gradients: Under the influence of a concentration gradient, ions diffuse from high-concentration regions to low-concentration regions in a concentration cell, altering the initial concentration gradient. This causes the measured potential difference to fail to accurately reflect the initial concentration difference, thus affecting the stability and accuracy of the measurement, especially under long-duration and high-concentration conditions. Reducing the diffusion effect requires shortening the measurement time, but this contradicts the need to obtain stable data.

[0138] Regarding measurement accuracy: The voltage difference in the external circuit caused by activity differences is small, typically only on the millivolt level. This requires extremely high precision in the test, as even tiny errors can significantly affect the results. The high technical requirements of the experimental equipment increase the complexity and operational difficulty of the experiment. Furthermore, in parallel experiments, each repetition requires emptying the electrolytic cell, refilling the electrolyte, and replacing the electrodes, which also increases the complexity of the experiment.

[0139] The test method proposed in this application solves the problems of liquid junction potential, diffusion caused by concentration difference, and test accuracy when measuring the ion activity of solution using concentration cells, thereby improving the accuracy and operability of the measurement.

[0140] In one embodiment, the oxidation potential of the reference material is lower than that of the working electrode, the counter electrode, and the solvent; the reduction potential of the reference material is higher than that of the working electrode, the counter electrode, and the solvent.

[0141] Understandably, to avoid interference, the electrochemical window of the reference material needs to cover the electrochemical reaction potential range of the working electrode, counter electrode, and solvent. The oxidation potential of the reference material should be lower than the oxidation potentials of the working electrode, counter electrode, and solvent. This ensures that the reference material is oxidized before the working electrode, counter electrode, and solvent, thus serving as a reference; that is, the oxidation potential of the reference material is measured by cyclic voltammetry. The reduction potential of the reference material should be higher than the reduction potentials of the working electrode, counter electrode, and solvent. This ensures that the reference material is reduced before the reduction of the working electrode, counter electrode, and solvent, thus serving as an internal control; that is, the reduction potential of the reference material is measured by cyclic voltammetry.

[0142] In one embodiment, the oxidation potential of the reference material is at least 0.1 V lower than the oxidation potentials of the working electrode, the counter electrode, and the solvent; the reduction potential of the reference material is at least 0.1 V higher than the reduction potentials of the working electrode, the counter electrode, and the solvent.

[0143] Typically, the oxidation potential of the reference material is required to be at least 0.1 V (100 mV) lower than the oxidation potentials of the working electrode, the counter electrode, and the solvent, and the reduction potential of the reference material is required to be at least 0.1 V (100 mV) higher than the reduction potentials of the working electrode, the counter electrode, and the solvent.

[0144] When testing the activity of salt in solution, the cation element of the target salt is metal element A, and the material of the counter electrode also includes metal A. It can be understood that the activity of the salt is essentially the activity of the salt cation; that is, the material of the counter electrode needs to have the same elemental composition as the cation being tested to meet the requirements. The electrode potential is expressed as follows: In order to ensure the accuracy of the final measured ion activity in the working solution, the redox potential of the reference substance and the redox potential of metal A must satisfy the above relationship. In this way, when using the working electrode to test the redox potential of the reference substance, it will not interfere with the counter electrode, thus improving the accuracy of the test.

[0145] In one embodiment, at least one of the following conditions is satisfied: Condition A: The redox potential range of the reference material relative to the standard hydrogen electrode is -3V to 1V; Condition B: The standard electrode potential of metal A relative to the standard hydrogen electrode is -4V to 1V; Condition C: The reference material includes metal compounds and / or metal complexes; Condition D: Metal A includes any one of lithium, zinc, magnesium, and calcium.

[0146] In one embodiment, the redox potential of the reference material relative to the standard hydrogen electrode meets the above-mentioned range. This improves the accuracy of the test.

[0147] In one embodiment, the standard electrode potential of metal A relative to the standard hydrogen electrode satisfies the above-mentioned range. This improves the accuracy of the test.

[0148] In one embodiment, the reference material includes a metal compound and / or a metal complex. It is understood that a metal compound refers to a compound formed by a metal element and other non-metallic elements or compounds, and a metal complex refers to a compound formed by a metal central ion (or atom) and a ligand capable of donating lone pairs of electrons through coordinate bonds. The ligands are typically organic or inorganic molecules capable of forming coordinate bonds with the metal center. The reference material with redox activity can be a metal compound and / or a metal complex.

[0149] In one embodiment, metal element A includes any one of lithium, zinc, magnesium, and calcium. For example, when the ion activity to be tested is lithium ion activity, that is, when the cation of the salt to be tested is lithium, metal element A is lithium.

[0150] In one embodiment, the metal compound includes a metallocene compound; and / or, the metal complex includes at least one of metalloporphyrin and metal pyridine.

[0151] It is understandable that metal compounds and metal complexes include the compounds mentioned above.

[0152] In one embodiment, the metallocene compound includes at least one of ferrocene, cobalt dicene, and nickel dicene; and / or, the metalloporphyrin includes at least one of nickel(II)porphyrin, nickel(III)porphyrin, cobalt(II)porphyrin, cobalt(III)porphyrin, and tetracarboxyphenylporphyrin cobalt; and / or, the metal pyridine includes a multidentate pyridine ligand complex.

[0153] Taking metallocene compounds as an example, metallocenes contain one transition metal atom and two cyclopentadiene ligands, forming a sandwich structure. Metallocene compounds exhibit good potential stability. Because the redox potential of the reference substance is also relatively stable, the measured potential essentially reflects the potential difference of the counter electrode in solutions at various salt concentrations. Among them, ferrocene, cobalt dicene, and nickel dicene have large delocalization charges and good stability, and are less affected by solvents and salts in solution, thus improving the accuracy of the test. Metalloporphyrins include at least one of nickel(II)porphyrin, nickel(III)porphyrin, cobalt(II)porphyrin, cobalt(III)porphyrin, and tetracarboxyphenylporphyrin cobalt. Metal pyridines include multidentate pyridine ligand complexes, which are organic ligands containing two or more pyridine rings as coordination sites. They can form stable coordination compounds with metal ions.

[0154] In one embodiment, the ferrocene comprises at least one of butylferrocene, 1,1'-dimethylferrocene, tert-butylferrocene, and ferrocene decane; and / or, the multidentate pyridine ligand comprises ruthenium(II) terpyridine.

[0155] Understandably, metallocene compounds possess large delocalization charges. The higher the degree of charge delocalization and the greater the steric hindrance, the better their stability. Butylferrocene, 1,1'-dimethylferrocene, tert-butylferrocene, and ferrocene decane are compounds with even higher degrees of charge delocalization and greater steric hindrance, exhibiting better solubility and stability in solution. This reduces the interference of environmental factors on potential measurements, thus providing a stable and reliable potential reference and improving measurement accuracy. Multidentate pyridine ligands include ruthenium(II) terpyridine.

[0156] In one embodiment, at least one of the following conditions is satisfied: Condition A: The concentration range of the reference substance is 1 mM to 100 mM; Condition B: The concentration range of the salt in the reference solution is 0.1 mM to 100 mM, and the concentration of the salt in the reference solution is equal to the value of a2; Condition C: The solvent includes an aprotic solvent; Condition D: The salt includes at least one of lithium salt, zinc salt, magnesium salt, and calcium salt; Condition E: The working electrode includes any one of Pt electrode, glassy carbon electrode, and carbon electrode.

[0157] In one embodiment, the concentration range of the reference substance is 1 mM to 100 mM. It is understood that the concentration of the reference substance affects the accuracy of the test, and that a concentration within the above range can improve the accuracy of the test.

[0158] The values ​​in the range of 1mM to 100mM include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 1mM, 5mM, 10mM, 20mM, 30mM, 40mM, 50mM, 60mM, 70mM, 80mM, 90mM, 100mM, 100mM, etc., as well as the range values ​​between any two of the above point values.

[0159] In one embodiment, the salt concentration in the reference solution ranges from 0.1 mM to 100 mM, and the salt concentration in the reference solution is equal to the value of a2. In this application, the reference solution is a solution with known activity. Typically, a lower concentration solution is chosen as the reference solution. Under low concentration conditions, the salt in the solution is approximately completely dissociated, and the activity is close to its concentration. Therefore, the activity of the salt in the low-concentration solution can be considered known. It is understood that different salts have different degrees of dissociation. In salt solutions with a high degree of dissociation, a concentration of 100 mM can be used as the reference solution, while in salt solutions with a low degree of dissociation, a concentration of 0.1 mM can be used as the reference solution.

[0160] The values ​​from 0.1mM to 100mM mentioned above include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.1mM, 0.5mM, 1mM, 5mM, 10mM, 20mM, 30mM, 40mM, 50mM, 60mM, 70mM, 80mM, 90mM, 100mM, 100mM, etc., as well as the range values ​​between any two of the above point values.

[0161] In one embodiment, the solvent includes an aprotic solvent. An aprotic solvent is one that does not contain free protons (hydrogen ions H+). + Solvents that do not form hydrogen bonds by releasing protons when dissolving the solute. Generally, some metals react readily in protic solvents; to reduce interference from the reaction on the electrode, solvents include aprotic solvents.

[0162] In one embodiment, the salt includes at least one selected from lithium salt, zinc salt, magnesium salt, and calcium salt.

[0163] In one embodiment, the working electrode includes any one of a Pt electrode, a glassy carbon electrode, and a carbon electrode. It is understood that the working electrode itself does not react and is an inert electrode.

[0164] In one embodiment, at least one of the following conditions is satisfied: Condition A: The aprotic solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; Condition B: The lithium salt anion includes PF6. - FSI - TFSI - At least one of them.

[0165] In one embodiment, the aprotic solvent includes at least one selected from ethylene carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. For example, in one embodiment, it is necessary to test the lithium salt activity of the electrolyte in a lithium-ion battery, and the solvent in the electrolyte includes ethylene carbonate and dimethyl carbonate.

[0166] In one embodiment, the lithium salt anion includes at least one of the above, TFSI - It is a bis(trifluoromethanesulfonyl)imide, FSI - It is a bis(fluorosulfonyl)imide.

[0167] In one embodiment, the redox potential of the reference material relative to the standard hydrogen electrode is within the redox window of the aprotic solvent relative to the standard hydrogen electrode. By ensuring that the redox potential of the reference material is within the redox window of the aprotic solvent, unnecessary oxidation or reduction of the solvent can be avoided, thereby improving the efficiency and stability of the electrochemical system.

[0168] In one embodiment, the step of performing cyclic voltammetry on the working electrode and counter electrode in a working solution to obtain the working potential E1 includes: forming a working electrolytic cell with the working electrode and counter electrode and the working solution; providing a diaphragm between the working electrode and counter electrode in the working electrolytic cell to divide the working electrolytic cell into a working electrode chamber and a counter electrode chamber; the working solution in the working electrode chamber includes a reference substance; connecting the working electrode and counter electrode to an electrochemical workstation; obtaining a working cyclic voltammetry curve on the electrochemical workstation; and obtaining the working potential E1 from the working cyclic voltammetry curve.

[0169] In the process of forming the test system, the working electrode and the counter electrode are inserted into the working solution to form a working electrolytic cell. A diaphragm is placed in the working electrolytic cell between the working electrode and the counter electrode to divide the working electrolytic cell into a working electrode chamber and a counter electrode chamber. The working solution in the working electrode chamber includes a reference substance, while the counter electrode chamber does not contain a reference substance to reduce the interference of the reference substance on the counter electrode. The working electrode and the counter electrode are connected to an electrochemical workstation, and the working cyclic voltammetry curve is obtained on the electrochemical workstation. The working potential E1 is obtained from the working cyclic voltammetry curve.

[0170] In other words, a diaphragm is placed between the working electrode and the counter electrode. The diaphragm can reduce the influence of the reference substance in the solution on the counter electrode potential, reduce the risk of electrode contamination, improve the measurement stability and reliability of the electrolytic cell, and ensure the accuracy of potential measurement.

[0171] In one embodiment, the step of performing cyclic voltammetry tests on the working electrode and the counter electrode in a reference solution to obtain a reference potential E2 includes: forming a reference electrolytic cell with the working electrode and the counter electrode and the reference solution; providing a diaphragm between the working electrode and the counter electrode in the reference electrolytic cell to divide the reference electrolytic cell into a working electrode chamber and a counter electrode chamber; the reference solution in the working electrode chamber includes a reference substance; connecting the working electrode and the counter electrode to an electrochemical workstation; obtaining a reference cyclic voltammetry curve on the electrochemical workstation; and obtaining the reference potential E2 from the reference cyclic voltammetry curve.

[0172] In other words, a diaphragm is placed between the working electrode and the counter electrode. The diaphragm can reduce the influence of the reference substance in the solution on the counter electrode potential, reduce the risk of electrode contamination, improve the measurement stability and reliability of the electrolytic cell, and ensure the accuracy of potential measurement.

[0173] In one embodiment, at least one of the following conditions is satisfied: Condition A: The electrolytic cell is an H-type electrolytic cell; Condition B: The membrane material includes at least one of porous polymer, ceramic, and glass fiber membrane.

[0174] In one embodiment, an H-type electrolytic cell design is employed, in which the working electrode and the counter electrode are placed in two separate chambers of the H-type electrolytic cell. The H-type electrolytic cell consists of a cathode chamber, an anode chamber, and an ion exchange membrane. This design allows two different chemical reactions to occur simultaneously in the separated chambers, while the ion exchange membrane allows ions to pass through to maintain charge balance. A reference substance is added to the solution on one side of the working electrode to reduce interference from the reference substance on the counter electrode.

[0175] In one embodiment, the diaphragm is made of at least one of the materials described above.

[0176] In one embodiment, at least one of the following conditions is satisfied: Condition A: In the step of performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the number of scan cycles in the cyclic voltammetry test is 3 to 100; Condition B: In the step of performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1Condition C: In the step of performing cyclic voltammetry on the working electrode and counter electrode in a reference solution to obtain the reference potential E2, the number of scan cycles in the cyclic voltammetry test is 3 to 100. Condition D: In the step of performing cyclic voltammetry on the working electrode and counter electrode in a reference solution to obtain the reference potential E2, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1 .

[0177] In one embodiment, in the step of performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the number of scans in the cyclic voltammetry test is 3 to 100.

[0178] During cyclic voltammetry testing, the random error in a single measurement is averaged through multiple scans to further improve measurement accuracy.

[0179] The values ​​in the range of 3 to 100 laps include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 3 laps, 5 laps, 10 laps, 20 laps, 30 laps, 40 laps, 50 laps, 60 laps, 70 laps, 80 laps, 90 laps, 100 laps, etc., as well as the range values ​​between any two of the above point values.

[0180] In one embodiment, in the step of performing cyclic voltammetry on the working electrode and the counter electrode in the working solution to obtain the working potential E1, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1 .

[0181] The above 0.1mV s -1 Up to 100mV s -1 In this context, the values ​​include the minimum and maximum values ​​within the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 0.1mV s. -1 0.5mVs -1 1mV s -1 5mV s -1 10mV s -1 20mV s -1 30mV s -1 40mV s -1 50mV s -1 60mV s -1 70mV s -1 80mV s -1 90mV s -1 100mV s -1And so on, as well as the range of values ​​between any two of the above point values.

[0182] In cyclic voltammetry, the scan rate can affect the kinetics of the electrode reaction. A slower scan rate allows sufficient time for the reaction to reach equilibrium, while a rapid scan may keep the reaction in a non-equilibrium state. Considering the differences in reaction kinetics among different solution systems, an appropriate scan rate can be selected within the above range to provide flexible and rapid experimental conditions to meet the needs of different systems.

[0183] In one embodiment, in the step of performing cyclic voltammetry on the working electrode and the counter electrode in a reference solution to obtain a reference potential E2, the number of scans in the cyclic voltammetry test is from 3 to 100.

[0184] During cyclic voltammetry testing, the random error in a single measurement is averaged through multiple scans to further improve measurement accuracy.

[0185] In one embodiment, in the step of performing cyclic voltammetry on the working electrode and the counter electrode in a reference solution to obtain the reference potential E2, the scan rate of the cyclic voltammetry test is 0.1 mV / s. -1 Up to 100mV s -1 .

[0186] Considering the differences in reaction kinetics among different solution systems, an appropriate scan rate can be selected within the above range to provide flexible and rapid experimental conditions to meet the needs of different systems.

[0187] In one embodiment, this application also provides a method for preparing a working curve of ion activity in solution, comprising: preparing a reference solution and working solutions of salts at different concentrations; testing the activity of metal A ions in the working solutions of salts at each concentration using a testing method as described above for testing the activity of ions in solution; and plotting a working curve of metal A ion activity versus salt concentration.

[0188] A working curve is a tool used in analytical chemistry for quantitative determination. This application describes a method for preparing a reference solution and working solutions of salts at different concentrations; using the aforementioned testing method, the activity of metal A ions in the working solutions of each salt concentration is tested; and a working curve is plotted between the activity of metal A ions and the concentration of the salt (the cation element of the salt is metal A). By inputting the salt concentration of the corresponding solution into the working curve, the activity of metal A ions at that salt concentration can be obtained.

[0189] In one embodiment, in the step of testing the activity of metal ion A in the working solution of each salt concentration using a test method, the activity of metal ion A in the working solution of each salt concentration is tested at least twice, with an interval of 1 min to 30 min between each test, and the average value and standard deviation of the activity are calculated.

[0190] The standard deviation is the square root of the mean of the squares of the differences between each value in a set of values ​​and the mean. It reflects the degree of dispersion of the values ​​in the dataset relative to the mean.

[0191] By repeating the test multiple times, the average value and standard deviation of the activity are calculated. If a data point in a set of values ​​deviates significantly from the average value during the test, that data point can be discarded and the test repeated to reduce errors and improve the accuracy of the test. Furthermore, the time interval between each test is within the above range to reduce the impact of unbalanced and unstable solutions.

[0192] In one embodiment, this application also provides an apparatus for testing the ion activity in solution as described above, comprising: an electrolytic cell containing a solution, the solution including a solvent, a redox-active reference substance and a salt, wherein the cation element of the salt includes a metal element A; a working electrode disposed in the electrolytic cell; a counter electrode disposed in the electrolytic cell, the material of the counter electrode including a metal A; and an electrochemical workstation including testing software, a working electrode interface and a counter electrode interface, the working electrode interface being connected to the working electrode and the counter electrode interface being connected to the counter electrode.

[0193] The above-mentioned device can be used to measure the ion activity in the test solution.

[0194] In one embodiment, this application also provides a method for testing the activity of lithium salt in a lithium-ion battery electrolyte. The method includes the method for testing the activity of ions in solution as described above, wherein the salt is a lithium salt and the material of the counter electrode is lithium metal.

[0195] Testing the activity of lithium ions in lithium salts within lithium-ion battery electrolytes is one of the key parameters for evaluating their performance. The activity of lithium ions in the electrolyte directly affects ion conductivity, thus influencing the overall performance and lifespan of the battery. The method described above can accurately test the activity of lithium ions in the electrolyte, providing a reliable basis for evaluating electrolyte performance.

[0196] Example

[0197] Activity test of lithium ions in electrolyte

[0198] Example 1

[0199] Prepare the reference solution (reference electrolyte).

[0200] A reference solution was prepared in an argon-filled glove box (O2, H2O < 0.1 ppm) using EC / DMC (1:1 volume ratio) as the solvent. 1 mM LiPF6 lithium salt was dissolved in the solvent, and the activity a1 (lithium ion activity) of the reference electrolyte was 1 mM.

[0201] Prepare the working solution (working electrolyte).

[0202] The working solution was prepared in an argon-filled glove box (O2, H2O < 0.1 ppm) using EC / DMC (1:1 volume ratio) as the solvent. A series of working solutions of lithium LiPF6 were prepared in the solvent with concentrations of 10 mM, 50 mM, 100 mM, 500 mM, 1 M, and 2 M of lithium LiPF6.

[0203] Prepare the working electrode: Pt electrode.

[0204] Prepare the counter electrode: a lithium metal sheet, 16 mm in diameter, 0.5 mm thick, and 99.9% pure.

[0205] Prepare a reference substance with redox activity: ferrocene.

[0206] Assemble the test device to test the operating potential E1

[0207] like Figure 2 As shown, in an electrolytic cell, 1 mM ferrocene was dissolved in 10 mM working electrolyte. Cyclic voltammetry tests were performed using lithium metal sheets and Pt electrodes as the counter and working electrodes in the electrochemical system, respectively, within a voltage range of 3 V to 4 V, at a rate of 10 mV / s. -1 The scan rate was adjusted, and a cyclic voltammetry test was performed every 5 minutes for 3 cycles, recording the results of the 3 cycles. The average value was used to obtain the working potential E1, and the measurement was repeated 6 times.

[0208] Assemble the test device to test the reference potential E2

[0209] like Figure 2 As shown, in an electrolytic cell, 1 mM ferrocene was dissolved in 1 mM standard electrolyte. Cyclic voltammetry tests were performed using lithium metal sheets and Pt electrodes as the counter and working electrodes in the electrochemical system, respectively, at 10 mV / s in the voltage range of 3 V to 4 V. -1 The scan rate was adjusted, and a cyclic voltammetry test was performed every 5 minutes for 3 cycles, recording the results of the 3 cycles. The average value was used to obtain the reference potential E2, and this was measured 6 times consecutively.

[0210] Data processing

[0211] According to the formula Substituting the measured operating potential E1, reference potential E2, and lithium ion activity a1 = 1 mM in the reference electrolyte into the above formula, where R is the gas constant (approximately 8.314 J / (mol·K)), T is the temperature (Kelvin), and z is the charge number in the battery reaction, F Given the Faraday constant (approximately 96485 C / mol), calculate the activity a2 of lithium ions in a 10 mM working electrolyte.

[0212] The activity a2 of lithium ions in working electrolytes of 50mM, 100mM, 500mM, 1M and 2M were tested sequentially using the above method. The activity-lithium salt concentration curve of lithium ions was plotted and the standard deviation of the 6 measurements was calculated.

[0213] Example 2

[0214] Based on Example 1, such as Figure 3 As shown, in an H-type electrolytic cell, the working electrode and counter electrode regions are separated by four layers of PP membrane. 1 mM ferrocene is injected only in the Pt working electrode region, while no ferrocene is injected in the counter electrode region where the lithium metal sheet is located. Cyclic voltammetry tests are then performed.

[0215] Comparative Example 1

[0216] The reference solution and working solution were prepared in the same manner as in Example 1.

[0217] Assemble a concentration cell: such as Figure 4 As shown, an H-type electrolytic cell is used, separated by four layers of PP membrane to minimize solute diffusion caused by concentration differences. Each chamber uses a high-purity (99.9%) lithium sheet with a diameter of 16 mm and a thickness of 0.5 mm as the electrode. The oxide layer on the surface is scraped off with a brush, and the cells are assembled in a glove box.

[0218] Measurement setup: A high-precision voltmeter was used to measure the potential difference ΔV. Six measurements were taken for each concentration pair, with a 5-minute interval between each measurement. The steady-state potential value was recorded after 30 minutes. The formula was used. Calculate the activity a2 of lithium ions in the working electrolyte, plot the lithium ion activity-lithium salt concentration curve, and calculate the standard deviation of 6 measurements.

[0219] Table 1 List of experimental parameters

[0220]

[0221]

[0222] Table 2 Test results of the examples and comparative examples

[0223]

[0224] From Tables 1 and 2 above, and Figure 5 The data shows that the lithium ion activity obtained by the test method of this application is closer to the lithium salt concentration and the standard deviation is smaller. This indicates that the activity obtained by the test method of this scheme is closer to the real situation, and the system of this scheme is more stable. Compared with the comparative scheme, the error is smaller and the accuracy is higher. In addition, the standard deviation of Example 2 is smaller than that of Example 1. Under high concentration conditions, the lithium ion activity in the lithium salt solution is closer to the lithium salt concentration. This shows that setting a diaphragm and adding a reference material only to the working electrode chamber can reduce the influence of the reference material on the lithium metal sheet electrode potential, reduce the risk of electrode contamination, improve the measurement stability and reliability of the electrolytic cell, and ensure the accuracy of potential measurement.

[0225] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method of testing the ionic activity in a solution, characterized in that, The method comprises: preparing a reference solution and a working solution, the reference solution and the working solution comprising a solvent, a redox-active reference substance, and a salt, the cation element of the salt comprising an A metal element; preparing a working electrode and a counter electrode, the material of the counter electrode comprising the A metal; carrying out cyclic voltammetry test on the working electrode and the counter electrode in the working solution to obtain a working potential E1; carrying out cyclic voltammetry test on the working electrode and the counter electrode in the reference solution to obtain a reference potential E2; According to the equation The activity of the A metal ions in the working solution, ai, is calculated, where a2 represents the activity of the A metal ions in the reference solution, R is the gas constant, T is the temperature, z is the number of charges in the cell reaction, and F is the Faraday constant.

2. The method of testing ionic activity in solution of claim 1, wherein, the oxidation potential of the reference substance is lower than the oxidation potential of the working electrode, the counter electrode, and the solvent; the reduction potential of the reference substance is higher than the reduction potential of the working electrode, the counter electrode, and the solvent.

3. The method of testing ionic activity in solution of claim 2, wherein, the oxidation potential of the reference substance is at least 0.1 V lower than the oxidation potential of the working electrode, the counter electrode, and the solvent; the reduction potential of the reference substance is at least 0.1 V higher than the reduction potential of the working electrode, the counter electrode, and the solvent.

4. The method for testing ionic activity in solution according to any one of claims 1 to 3, characterized in that, At least one of the following conditions is met: Condition A: the redox potential of the reference substance relative to the standard hydrogen electrode is in the range of -3 V to 1 V; Condition B: the standard electrode potential of the A metal relative to the standard hydrogen electrode is in the range of -4 V to 1 V; Condition C: the reference substance comprises a metal compound and / or a metal complex; Condition D: the A metal element comprises any one of lithium, zinc, magnesium, and calcium.

5. The method of testing ionic activity in solution of claim 4, wherein, The metal compound comprises a metallocene compound; and / or, the metal complex comprises at least one of a metal porphyrin and a metal pyridine.

6. The method of testing ionic activity in solution of claim 5, wherein, The metallocene compound comprises at least one of ferrocene, cobaltocene, and nickelocene; and / or, the metal porphyrin comprises at least one of nickel(II) porphyrin, nickel(III) porphyrin, cobalt(II) porphyrin, cobalt(III) porphyrin, and tetra-carboxyphenyl porphyrin cobalt; and / or, the metal pyridine comprises a multidentate pyridine ligand complex.

7. The method of testing ionic activity in solution of claim 6, wherein, The ferrocene comprises at least one of butylferrocene, 1,1'-dimethylferrocene, t-butylferrocene, and ferrocene decane; and / or, the multidentate pyridine ligand comprises trispyridine ruthenium(II).

8. The method of testing ionic activity in solution according to any one of claims 1 to 7, wherein, At least one of the following conditions is met: Condition A: the concentration of the reference substance is in the range of 1 mM to 100 mM; Condition B: the concentration of the salt in the reference solution is in the range of 0.1 mM to 100 mM, and the concentration of the salt in the reference solution is equal to the value of a2; Condition C: the solvent comprises an aprotic solvent; Condition D: the salt comprises at least one of a lithium salt, a zinc salt, a magnesium salt, and a calcium salt; Condition E: the working electrode comprises any one of a Pt electrode, a glassy carbon electrode, and a carbon electrode.

9. The method of testing ionic activity in solution of claim 8, wherein, At least one of the following conditions is met: Condition A: the aprotic solvent comprises at least one of ethylene carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; Condition B: the anion of the lithium salt comprises at least one of PF6 — , FSI — , TFSI — ​ Condition C: the redox potential of the reference substance relative to the standard hydrogen electrode is within the redox window of the aprotic solvent relative to the standard hydrogen electrode.

10. The method of testing ionic activity in solution according to any one of claims 1 to 9, wherein, In the step of performing cyclic voltammetry test on the working electrode and the counter electrode in the working solution to obtain a working potential E1, comprising: forming a working electrolytic cell with the working electrode and the counter electrode and the working solution, a diaphragm is arranged between the working electrode and the counter electrode to separate the working electrolytic cell into a working electrode chamber and a counter electrode chamber, the working solution in the working electrode chamber comprises the reference substance; connecting the working electrode and the counter electrode to an electrochemical workstation to obtain a working cyclic voltammetry curve, and obtaining the working potential E1 in the working cyclic voltammetry curve.

11. The method of testing ionic activity in solution according to any one of claims 1 to 10, wherein, In the step of performing cyclic voltammetry test on the working electrode and the counter electrode in the reference solution to obtain a reference potential E2, comprising: forming a reference electrolytic cell with the working electrode and the counter electrode and the reference solution, a diaphragm is arranged between the working electrode and the counter electrode to separate the reference electrolytic cell into a working electrode chamber and a counter electrode chamber, the reference solution in the working electrode chamber comprises the reference substance; connecting the working electrode and the counter electrode to an electrochemical workstation to obtain a reference cyclic voltammetry curve, and obtaining the reference potential E2 in the reference cyclic voltammetry curve.

12. The method for testing ionic activity in solution according to claim 10 or 11, characterized in that, At least one of the following conditions is met: Condition A: the electrolytic cell is an H-type electrolytic cell; Condition B: the material of the diaphragm comprises at least one of porous polymer, ceramic, and glass fiber diaphragm.

13. The method for testing ionic activity in solution according to any one of claims 1 to 12, characterized in that, At least one of the following conditions is met: Condition A: in the step of performing cyclic voltammetry test on the working electrode and the counter electrode in the working solution to obtain a working potential E1, the number of scanning cycles of the cyclic voltammetry test is 3 to 100 cycles; Condition B: in the step of subjecting the working electrode and the counter electrode to cyclic voltammetry test in the working solution to obtain the working potential E1, the scan rate of the cyclic voltammetry test is 0.1 mV s -1 to 100 mV s -1 ; Condition C: in the step of performing cyclic voltammetry test on the working electrode and the counter electrode in the reference solution to obtain a reference potential E2, the number of scanning cycles of the cyclic voltammetry test is 3 to 100 cycles; Condition D: in the step of performing cyclic voltammetry test on the working electrode and the counter electrode in the reference solution to obtain the reference potential E2, the scan rate of the cyclic voltammetry test is 0.1 mV s -1 to 100 mV s -1 .

14. A method of preparing a working curve of ion activity in solution, characterized in that, comprising: preparing a reference solution and working solutions of different concentrations of salt; testing the activity of the A metal ion in the working solution of each concentration of salt by a test method, the test method being the test method for the activity of the ion in the solution as claimed in any one of claims 1 to 12; plotting a working curve of the activity of the A metal ion versus the concentration of the salt.

15. The method of preparing a working curve of ion activity in solution according to claim 14, characterized in that, In the step of testing the activity of the A metal ion in the working solution of each concentration of salt by a test method, the activity of the A metal ion in the working solution of each concentration of salt is tested at least twice, and the time interval between each test is 1 min to 30 min, and the average value and the standard deviation of the activity of the A metal ion are calculated.

16. A device for the testing of the ionic activity of a solution as claimed in any one of claims 1 to 15, characterised in that, comprising: an electrolytic cell containing a solution, the solution comprising a solvent, a redox-active reference substance, and a salt, the cation element of the salt comprising an A metal element; a working electrode arranged in the electrolytic cell; a counter electrode arranged in the electrolytic cell, the material of the counter electrode comprising the A metal; An electrochemical workstation comprising test software, a working electrode interface that connects the working electrode, and a counter electrode interface that connects the counter electrode.

17. A method of testing the activity of lithium ions in a lithium-ion battery electrolyte, characterized in that, The test method comprises the test method for ion activity in solution as claimed in any one of claims 1 to 16, the salt is a lithium salt, and the material of the counter electrode is lithium metal.

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