Method and equipment for predicting solution loss potential of electrochemical lithium extraction electrode and application

Abstract

The invention relates to a method for predicting the solution loss potential of an electrochemical lithium extraction electrode. The method comprises the following steps: acquiring steady-state diffusion coefficients of the lithium extraction electrode under different lithium ion concentrations by adopting a constant-current electrochemical impedance spectroscopy (EIS) test; the solution loss potentials of the lithium extraction electrode under different lithium ion concentrations are obtained; on the basis of the obtained steady-state diffusion coefficient and the solution loss potential, fitting to obtain a function relation between the steady-state diffusion coefficient and the solution loss potential; in the electrochemical lithium extraction process, the steady-state diffusion coefficient of the lithium extraction electrode is measured in real time, and the solution loss potential of the lithium extraction electrode is calculated in real time through the obtained function relation between the solution loss potential of the lithium extraction electrode and the diffusion coefficient. The invention further relates to equipment for predicting the solution loss potential of the electrochemical lithium extraction electrode and application. The method and equipment are high in integration degree and simple and convenient to operate, the solution loss potential of the electrode under different lithium ion concentrations can be accurately predicted, the electrode potential can be regulated and controlled in real time, and the cycling stability of electrochemical lithium extraction is improved.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical lithium extraction, and in particular, relates to a method, a device and an application for predicting the dissolution loss potential of an electrochemical lithium extraction electrode. Background Art

[0002] Lithium is widely used in various fields from energy storage devices to industrial manufacturing and aerospace engineering due to its advantages of low atomic mass and high electrode potential. Therefore, the development of efficient lithium extraction technology has received widespread attention. Compared with the high energy consumption and high environmental footprint of solid mineral lithium extraction methods such as spodumene and lepidolite, lithium-containing solutions, especially salt lake brines, are considered to be an ideal source of lithium for large-scale production due to their abundant resources and low environmental pollution during the lithium extraction process. However, due to the high concentration of Na in China's salt lake brines, the + / Li + or Mg 2+ / Li + The proportion is extremely high, and more advanced technologies are needed in the process of lithium extraction to achieve selective and efficient extraction. Compared with membrane separation, electrodialysis and solvent extraction, lithium extraction technology based on electrochemical redox has become a new generation of technology for efficient and selective extraction of lithium from lithium-containing solutions due to its high lithium embedding ability, selectivity and recovery rate.

[0003] However, the electrode dissolution problem is currently the main obstacle limiting the industrial application of electrochemical lithium extraction. In the process of selective lithium extraction, as the lithium concentration in the main solution decreases, the concentration polarization phenomenon inside the membrane electrode intensifies, the lithium ion diffusion resistance increases, and electrode dissolution is likely to occur; and if the operating potential remains unchanged at this time, the dissolution will be further aggravated, resulting in a significant decrease in the cycle stability of the entire system. Therefore, the ideal situation is to be able to adjust the electrode potential in real time, but at present, the change in the dissolution potential of the lithium extraction electrode under different lithium ion concentration conditions is still unclear and the acquisition process is complicated, which greatly limits the large-scale industrial application of electrochemical lithium extraction in extracting lithium from lithium-containing solutions.

[0004] Therefore, it is urgent to develop a method and equipment that can accurately predict the dissolution potential of the electrochemical lithium extraction electrode during the electrochemical extraction of lithium from a lithium-containing solution, so as to solve the dissolution problem caused by the unknown dissolution potential during the lithium extraction process at different lithium concentrations. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method, equipment and application that can accurately predict the dissolution potential of electrochemical lithium extraction electrodes, find the potential conditions under which electrode dissolution does not occur or rarely occurs, and achieve a significant reduction in the dissolution loss of lithium extraction electrodes during the electrochemical lithium extraction process.

[0006] The method of the present invention establishes for the first time a functional relationship between the dissolution potential of a lithium extraction electrode and the steady-state diffusion coefficient during electrochemical lithium extraction. The method can accurately predict the dissolution potential of a lithium extraction electrode under different lithium ion concentrations, and can be used to regulate the electrode potential during electrochemical lithium extraction in real time, so that the lithium extraction electrode works under conditions of minimal dissolution, thereby significantly reducing the dissolution loss of the lithium extraction electrode during electrochemical lithium extraction from a lithium-containing solution.

[0007] To achieve the purpose of the present invention, the method for predicting the electrochemical lithium extraction electrode dissolution potential of the present invention specifically adopts a technical solution comprising the following steps:

[0008] Step S1: Obtaining the steady-state diffusion coefficient of the lithium-extracting electrode at different lithium ion concentrations

[0009] The steady-state diffusion coefficient of the lithium-extracting electrode at different lithium ion concentrations was obtained by constant current electrochemical impedance spectroscopy (EIS) test. The operating conditions were: frequency range 0.001~1*10 6 Hz, current is less than 1mA;

[0010] Step S2: Obtaining the dissolution potential of the lithium-extracting electrode at different lithium ion concentrations

[0011] In this step, an unactivated lithium extraction electrode is used as an anode and an electrochemically oxidized activated lithium extraction electrode is used as a cathode, and a reference electrode is set at the cathode, the cathode liquid is a lithium-containing solution, and the anode liquid is a lithium-containing conductive solution;

[0012] S2-1: Obtain the estimated range of lithium extraction electrode dissolution potential

[0013] A constant current is applied to the cathode liquid, and a point test is performed during the process of potential reduction until electrode dissolution occurs. The experiment is repeated at different lithium ion concentrations to obtain the estimated range of potential loss of the lithium extraction electrode at different concentrations.

[0014] S2-2: Obtain the accurate value of the lithium extraction electrode dissolution potential

[0015] A constant current is applied to the cathode liquid. When the electrode potential reaches a set value within the estimated range of the dissolution potential of the lithium extraction electrode, a constant potential is applied to the lithium extraction electrode to observe whether dissolution occurs. If not, the applied constant potential is changed in a gradient until electrode dissolution is observed. The experiment is repeated at different lithium ion concentrations to obtain accurate dissolution potentials at different lithium ion concentrations.

[0016] Step S3: Establishing the functional relationship between the lithium extraction electrode dissolution potential and the steady-state diffusion coefficient

[0017] Based on the steady-state diffusion coefficient obtained in step S1 and the dissolution potential obtained in step S2, a functional relationship between the dissolution potential and the diffusion coefficient of the lithium extraction electrode under different lithium ion concentrations is obtained by fitting;

[0018] Step S4: Real-time prediction of the dissolution potential of the lithium electrode

[0019] During the electrochemical lithium extraction process, the steady-state diffusion coefficient of the lithium extraction electrode is measured in real time, and the dissolution potential of the lithium extraction electrode is calculated in real time according to the functional relationship between the dissolution potential of the lithium extraction electrode and the diffusion coefficient obtained in step S3.

[0020] After accurately obtaining the dissolution potential of the lithium extraction electrode through calculation, the dissolution loss of the lithium extraction electrode can be reduced by real-time regulation of the applied electrode potential, so that the lithium extraction electrode can work under the condition of minimum dissolution loss, thereby significantly reducing the dissolution loss of the lithium extraction electrode during the electrochemical extraction of lithium from lithium-containing solutions, and effectively improving the cycle stability of electrochemical lithium extraction.

[0021] Preferably, the lithium extraction electrode described in the present application may be an electrochemical lithium extraction electrode commonly used in the art, preferably a lithium manganate electrode, a lithium iron phosphate electrode or a lithium titanate electrode.

[0022] Preferably, the anolyte described in the present application is a solution of lithium chloride, lithium bromide, lithium fluoride, lithium nitrate, lithium acetate, lithium oxalate, lithium sulfate, lithium acetate or lithium formate with a concentration of 0.01-1 M. Between any two embodiments of the present application, the anolyte used can be used interchangeably.

[0023] Preferably, in steps S1-S4, a lithium-containing solution having a certain lithium ion concentration is used as the cathode liquid for the experiment, and the lithium ion concentration in the lithium-containing solution can be 0-2000 mg / L. The lithium-containing solution of the present application can be any lithium-containing solution. + Compound preparation, such as LiCl, or can simulate the main Li + 、Na + , K + , Ca 2+ Mg 2+ The plasma is prepared by mixing lithium-rich salt lake brine components, for example, LiCl with MgCl2, CaCl2, KCl, NaCl, Na2SO4, K2SO4, MgSO4, etc.

[0024] Preferably, in the constant current electrochemical impedance spectroscopy test of step S1, the lithium extraction electrode after electrochemical oxidation activation is used as the working electrode (i.e., cathode), preferably lithium manganese oxide, lithium iron phosphate, and lithium titanate electrodes are used as the working electrode, and the cathode liquid is a lithium-containing solution with a certain lithium ion concentration; the counter electrode uses the electrochemical lithium extraction electrode counter electrode commonly used in the art, and the electrode matrix material can be an inert metal and / or a non-metallic conductive material. Optionally, the electrode matrix material includes one or more conductive electrodes such as graphite sheets, titanium sheets, carbon cloth, carbon felt, platinum sheets, gold sheets, silver sheets, copper sheets, and aluminum sheets; a reference electrode can also be set at the same time.

[0025] Preferably, the reference electrode in steps S1 and S2 can be a commonly used reference electrode in the art, such as a KCl-saturated Ag / AgCl reference electrode, a saturated calomel electrode, a mercury oxide electrode and a mercurous sulfate electrode, preferably a KCl-saturated Ag / AgCl reference electrode.

[0026] Preferably, the constant current in step S2 is in the range of 1-50 mA.

[0027] Preferably, the potential value is tested at a point with a gradient of ≤-0.1 V in step S2-1, and a constant potential is applied to the lithium extraction electrode in step S2-1 with a gradient of ≤-0.02 V. Generally speaking, the smaller the gradient, the more accurate the measurement value.

[0028] The present invention also provides a device for predicting the dissolution potential of an electrochemical lithium extraction electrode, which comprises:

[0029] an electrode set, which consists of a working electrode, a counter electrode and a reference electrode;

[0030] EIS real-time monitor, used to measure the steady-state diffusion coefficient of the working electrode in real time;

[0031] A data analyzer, used to calculate the dissolution potential of the working electrode in real time;

[0032] The electrode potential responder is used to adjust the potential of the working electrode in real time.

[0033] The working electrode is the lithium extraction electrode mentioned above in the present application, which can be an electrochemical lithium extraction electrode commonly used in the art, preferably a lithium manganate electrode, a lithium iron phosphate electrode or a lithium titanate electrode.

[0034] The data analyzer uses the steady-state diffusion coefficient value of the lithium extraction electrode measured in real time by the EIS real-time monitor to perform a functional relationship operation between the lithium extraction electrode dissolution potential and the diffusion coefficient obtained in the method for predicting the electrochemical lithium extraction electrode dissolution potential, and obtains the dissolution potential of the lithium extraction electrode in real time.

[0035] The present invention also provides the application of the device for predicting the dissolution loss potential of the electrochemical lithium extraction electrode in extracting lithium from a lithium-containing solution, especially in extracting lithium from lithium-containing salt lake brine.

[0036] Compared with the prior art, the present invention establishes a functional relationship between the dissolution potential of a lithium extraction electrode and the steady-state diffusion coefficient of lithium ions in a lithium extraction solution, provides a method, device and application for predicting the dissolution potential of an electrochemical lithium extraction electrode, and solves the problem of aggravated dissolution caused by the unknown dissolution potential of the lithium extraction electrode in the lithium extraction process with a constantly changing lithium concentration. This is of great significance to the application of electrochemical lithium extraction in my country, especially the sustainable development of the salt lake lithium extraction industry and the new energy industry.

[0037] At the same time, the method and equipment for predicting the dissolution potential of the electrochemical lithium extraction electrode of the present invention have a high degree of integration and are easy to operate. It is only necessary to measure the steady-state diffusion coefficient of the lithium extraction electrode in the process of electrochemical lithium extraction, and the electrode dissolution potential under different lithium ion concentrations can be accurately predicted through the functional relationship between the dissolution potential of the lithium extraction electrode and the steady-state diffusion coefficient, thereby achieving real-time regulation of the electrode potential, improving the cycle stability of electrochemical lithium extraction, and laying a good foundation for the industrial application of electrochemical lithium extraction from lithium-containing solutions, especially lithium extraction from salt lake brine. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the specific implementation modes of the present invention, the drawings required for use in the description of the specific implementation modes will be briefly introduced below. Obviously, the drawings in the following description are some implementation modes of the present invention. For ordinary technicians in this field, other implementation modes can be obtained based on these drawings without paying creative work.

[0039] Figure 1 The process roadmap of the method for predicting the dissolution loss potential of the electrochemical lithium extraction electrode of the present invention is shown;

[0040] Figure 2 The schematic diagram of the connection of the device for predicting the dissolution potential of the electrochemical lithium extraction electrode of the present invention is shown;

[0041] Figure 3 A graph showing the relationship between the dissolution potential of lithium manganate and the steady-state diffusion coefficient is shown;

[0042] Figure 4 The relationship between the dissolution potential of lithium manganate and the transient diffusion coefficient is shown;

[0043] Figure 5 shows the relationship between the dissolution potential of lithium iron phosphate and the steady-state diffusion coefficient;

[0044] Figure 6 A graph showing the relationship between the lithium iron phosphate dissolution potential and the transient diffusion coefficient is shown;

[0045] Figure 7 A graph showing the relationship between the dissolution potential of lithium titanate and the steady-state diffusion coefficient is shown;

[0046] Figure 8 A graph showing the relationship between the dissolution potential of lithium titanate and the transient diffusion coefficient is shown. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] As is well known, the dissolution problem is the main obstacle to the industrial application of electrochemical lithium extraction technology in the extraction of lithium from lithium-containing solutions through efficient electrochemical ion exchange (ESIX). In the process of selective lithium extraction, concentration polarization continues to intensify, and the lithium concentration in the lithium-containing bulk solution continues to decrease. If the potential applied to the lithium extraction electrode is not appropriate, it will cause significant electrode dissolution. In order to study the dissolution mechanism of lithium extraction electrodes at different lithium concentrations, the inventors conducted a large number of experiments and found that under high overpotentials (high over-potential) and low overpotentials (low over-potential), the lithium insertion and delithiation of the electrode pair are controlled by internal diffusion, thereby realizing that the diffusion coefficient (D) is a key parameter in the electrochemical lithium extraction process. Further, according to Fick's law, the relationship between the diffusion coefficient and the lithium ion concentration can be obtained, and it is speculated whether the electrode dissolution potential and the lithium ion concentration can be related through the diffusion coefficient. The diffusion coefficient includes a steady-state diffusion coefficient and a transient diffusion coefficient, which can be measured by constant current electrochemical impedance spectroscopy test (EIS) and constant voltage step test (CA), respectively. After more experiments and verifications, the inventors finally found that the electrode diffusion coefficient calculated by EIS and CA can be used as a bridge to associate the electrode dissolution potential with the lithium ion concentration in a clear functional relationship. After data fitting, it was found that the electrode dissolution potential was inversely proportional to the lithium ion concentration, and the result of fitting with the steady-state diffusion coefficient was better than the result of fitting with the transient diffusion coefficient. Therefore, the method for predicting the electrochemical lithium extraction electrode dissolution potential of the present invention chooses to use the steady-state diffusion coefficient and the electrode dissolution potential under different lithium ion concentrations to fit the functional relationship.

[0049] The following examples 1-3 and comparative examples 1-3 respectively use lithium manganese oxide, lithium iron phosphate, and lithium titanate as working electrodes to illustrate the use of Figure 1 The method of the present invention shown in the figure is a method of fitting with a steady-state diffusion coefficient to obtain a functional relationship for predicting the dissolution potential of an electrochemical lithium extraction electrode. At the same time, an experiment using a transient diffusion coefficient for fitting was performed to compare with the method of the present invention using a steady-state diffusion coefficient for fitting.

[0050] Example 1

[0051] Obtain the relationship between the dissolution potential and steady-state diffusion coefficient of lithium manganate electrode

[0052] The activated lithium manganate electrode was used as the cathode, the titanium plate as the counter electrode, the KCl-saturated Ag / AgCl electrode as the reference electrode, and the cathode liquid was a lithium-containing solution with a lithium ion concentration of 100, 50, 20, and 10 mg / L. Constant current electrochemical impedance spectroscopy tests were performed at different lithium ion concentrations at a frequency of 0.001 to 1*10 6 Hz, the current was 0.05 mA, and the steady-state diffusion coefficient of the lithium manganate electrode at different lithium ion concentrations was obtained;

[0053] The activated lithium manganate electrode was used as the cathode, and the unactivated lithium manganate electrode was used as the anode. The cathode liquid was a lithium-containing solution with a lithium ion concentration of 100, 50, 20, and 10 mg / L, respectively, and a pH of 7. The anode liquid was a 0.01 M LiCl solution. First, a constant current of 50 mA was applied to a 100 mg / L cathode liquid, and during the potential reduction process, point tests were taken at different potential points with a gradient of -0.1 V until electrode dissolution occurred, and then the experiment was repeated at lithium ion concentrations of 50, 20, and 10 mg / L, and the estimated range of dissolution potential of lithium manganate electrode at different lithium ion concentrations was measured to be 0.3-0.8 V; then, a constant current of 50 mA was applied to a 100 mg / L cathode liquid, and when the electrode potential reached 0.3 V, the constant current was stopped, and a constant potential of 0.3 V was applied to the cathode to observe whether dissolution occurred. If not, the experiment was repeated with a gradient of -0.02 V until electrode dissolution was observed, and then the experiment was repeated at lithium ion concentrations of 50, 20, and 10 mg / L and at constant potentials of 0.5 V, 0.6 V, and 0.8 V to obtain accurate electrode dissolution potentials at different lithium ion concentrations;

[0054] Mathematical software was used to fit the steady-state diffusion coefficient and electrode dissolution potential of the lithium manganate electrode at different lithium ion concentrations. The fitting results are shown in Figure 3 As shown, the functional relationship between the steady-state diffusion coefficient and electrode dissolution potential of the lithium manganate electrode under different lithium ion concentrations is obtained as follows:

[0055] D=2.160E-6E MD -1 -2.016E-6

[0056] Where D is the steady-state diffusion coefficient of the lithium manganate electrode, E MD is the dissolution potential of the lithium manganate electrode.

[0057] from Figure 3 It can be seen that the dissolution potential of the lithium manganese oxide electrode has a good inverse proportional functional relationship with the steady-state diffusion coefficient.

[0058] Comparative Example 1

[0059] Obtain the relationship between the dissolution potential of lithium manganate electrode and the transient diffusion coefficient

[0060] The experiment of Example 1 was repeated, except that the constant current electrochemical impedance spectroscopy test was changed to a constant voltage step test, and the transient diffusion coefficient of the lithium manganese oxide electrode was obtained. The transient diffusion coefficient of the lithium manganese oxide electrode and the electrode dissolution potential under different lithium ion concentrations were fitted. The fitting results are shown in FIG. Figure 4 As shown, the functional relationship between the transient diffusion coefficient and electrode dissolution potential of the lithium manganate electrode at different lithium ion concentrations is obtained as follows:

[0061] D=5.839E-7E MD -1 +8.685E-6

[0062] Where D is the transient diffusion coefficient of the lithium manganese oxide electrode, E MD is the dissolution potential of the lithium manganate electrode.

[0063] from Figure 4 It can be seen that the fitting results of the dissolution potential and transient diffusion coefficient of the lithium manganese oxide electrode are poor, and the ideal functional relationship between the diffusion coefficient and the dissolution potential cannot be obtained.

[0064] Example 2

[0065] Obtain the relationship between the dissolution potential and steady-state diffusion coefficient of lithium iron phosphate electrode

[0066] The activated lithium iron phosphate electrode was used as the cathode, the titanium plate as the counter electrode, the KCl-saturated Ag / AgCl electrode as the reference electrode, and the cathode liquid was a lithium-containing solution with lithium ion concentrations of 100, 50, 20, and 10 mg / L, respectively. Constant current electrochemical impedance spectroscopy tests were performed at different lithium ion concentrations at a frequency of 0.001 to 1*10 6 Hz, the current was 0.05 mA, and the steady-state diffusion coefficient of the lithium iron phosphate electrode at different lithium ion concentrations was obtained;

[0067] The activated lithium iron phosphate electrode was used as the cathode, and the unactivated lithium iron phosphate electrode was used as the anode. The cathode liquid was a lithium-containing solution with lithium ion concentrations of 100, 50, 20, and 10 mg / L, respectively, and the pH was 5. The anode liquid was a 0.01 M LiCl solution. First, a constant current of 50 mA was applied to a 100 mg / L cathode solution, and during the potential reduction process, point tests were taken at different potential points with a gradient of -0.1 V until electrode dissolution occurred. The experiment was then repeated at lithium ion concentrations of 50, 20, and 10 mg / L, and the estimated range of lithium iron phosphate electrode dissolution potentials at different lithium ion concentrations was measured to be 0.4-0.9 V. Then, a constant current of 50 mA was applied to a 100 mg / L cathode solution. When the electrode potential reached 0.4 V, the constant current was stopped, and a constant potential of 0.4 V was applied to the cathode to observe whether dissolution occurred. If not, the experiment was repeated with a gradient of -0.02 V until electrode dissolution was observed. The experiment was then repeated at lithium ion concentrations of 50, 20, and 10 mg / L and at constant potentials of 0.6 V, 0.7 V, and 0.9 V to obtain accurate electrode dissolution potentials at different lithium ion concentrations.

[0068] Mathematical software was used to fit the steady-state diffusion coefficient and electrode dissolution potential of lithium iron phosphate electrode at different lithium ion concentrations. The fitting results are shown in Figure 5 As shown, the functional relationship between the steady-state diffusion coefficient and electrode dissolution potential of the lithium manganate electrode under different lithium ion concentrations is obtained as follows:

[0069] D=2.904E-6E MD -1 -2.531E-6

[0070] Where D is the steady-state diffusion coefficient of the lithium iron phosphate electrode, E MD is the dissolution potential of the lithium iron phosphate electrode.

[0071] from Figure 5 It can be seen that the dissolution potential of the lithium iron phosphate electrode has a good inverse proportional functional relationship with the steady-state diffusion coefficient.

[0072] Comparative Example 2

[0073] Obtain the relationship between the dissolution potential and transient diffusion coefficient of lithium iron phosphate electrode

[0074] The experiment of Example 2 was repeated, except that the constant current electrochemical impedance spectroscopy test was changed to a constant voltage step test, and the transient diffusion coefficient of the lithium iron phosphate electrode was obtained. The transient diffusion coefficient of the lithium iron phosphate electrode and the electrode dissolution potential under different lithium ion concentrations were fitted. The fitting results are shown in FIG. Figure 6 As shown, the functional relationship between the transient diffusion coefficient and electrode dissolution potential of the lithium iron phosphate electrode at different lithium ion concentrations is obtained as follows:

[0075] D=2.683E-6E MD -1 +2.096E-6

[0076] Where D is the transient diffusion coefficient of the lithium iron phosphate electrode, E MD is the dissolution potential of the lithium iron phosphate electrode.

[0077] from Figure 6 It can be seen that the fitting results of the dissolution potential and transient diffusion coefficient of the lithium iron phosphate electrode are poor, and the ideal functional relationship between the diffusion coefficient and the dissolution potential cannot be obtained.

[0078] Example 3

[0079] Obtain the relationship between the dissolution potential and steady-state diffusion coefficient of lithium titanate electrode

[0080] The activated lithium titanate electrode was used as the cathode, the titanium plate as the counter electrode, the KCl-saturated Ag / AgCl electrode as the reference electrode, and the cathode liquid was a lithium-containing solution with lithium ion concentrations of 100, 50, 20, and 10 mg / L, respectively. Constant current electrochemical impedance spectroscopy tests were performed at different lithium ion concentrations at a frequency of 0.001 to 1*10 6 Hz, the current was 0.05 mA, and the steady-state diffusion coefficient of the lithium titanate electrode at different lithium ion concentrations was obtained;

[0081] The activated lithium titanate electrode was used as the cathode, and the unactivated lithium titanate electrode was used as the anode. The cathode liquid was a lithium-containing solution with a lithium ion concentration of 100, 50, 20, and 10 mg / L, respectively, and a pH of 7. The anode liquid was a 0.01 M LiCl solution. First, a constant current of 50 mA was applied to a 100 mg / L cathode liquid, and during the potential reduction process, point tests were taken at different potential points with a gradient of -0.1 V until electrode dissolution occurred. The experiment was then repeated at lithium ion concentrations of 50, 20, and 10 mg / L, and the estimated range of lithium titanate electrode dissolution potential at different lithium ion concentrations was measured to be 0.1-0.6 V. Then, a constant current of 50 mA was applied to a 100 mg / L cathode liquid, and when the electrode potential reached 0.1 V, the constant current was stopped, and a constant potential of 0.1 V was applied to the cathode to observe whether dissolution occurred. If not, the experiment was repeated with a gradient of -0.02 V until electrode dissolution was observed. The experiment was then repeated at lithium ion concentrations of 50, 20, and 10 mg / L and constant potentials of 0.3 V, 0.4 V, and 0.6 V to obtain accurate electrode dissolution potentials at different lithium ion concentrations.

[0082] Mathematical software was used to fit the steady-state diffusion coefficient and electrode dissolution potential of lithium titanate electrode at different lithium ion concentrations. The fitting results are shown in Figure 7As shown, the functional relationship between the steady-state diffusion coefficient and electrode dissolution potential of the lithium manganate electrode under different lithium ion concentrations is obtained as follows:

[0083] D=1.386E-6E MD -1 +5.152E-7

[0084] Where D is the steady-state diffusion coefficient of the lithium titanate electrode, E MD is the dissolution potential of lithium titanate electrode.

[0085] from Figure 7 It can be seen that the dissolution potential of the lithium titanate electrode has a good inverse proportional functional relationship with the steady-state diffusion coefficient.

[0086] Comparative Example 3

[0087] Obtain the relationship between the dissolution potential and transient diffusion coefficient of lithium titanate electrode

[0088] The experiment of Example 2 was repeated, except that the constant current electrochemical impedance spectroscopy test was changed to a constant voltage step test, and the transient diffusion coefficient of the lithium titanate electrode was obtained. The transient diffusion coefficient of the lithium titanate electrode and the electrode dissolution potential at different lithium ion concentrations were fitted. The fitting results are shown in FIG. Figure 8 As shown, the functional relationship between the transient diffusion coefficient and electrode dissolution potential of the lithium titanate electrode at different lithium ion concentrations is obtained as follows:

[0089] D=1.308E-7E MD -1 +3.338E-6

[0090] Where D is the transient diffusion coefficient of the lithium titanate electrode, E MD is the dissolution potential of lithium titanate electrode.

[0091] from Figure 8 It can be seen that the fitting results of the dissolution potential and transient diffusion coefficient of the lithium titanate electrode are poor, and the ideal functional relationship between the diffusion coefficient and the dissolution potential cannot be obtained.

[0092] From the results of Examples 1-3 and Comparative Examples 1-3, it can be clearly seen that the results of fitting using the steady-state diffusion coefficient are significantly better than the results of fitting using the transient diffusion coefficient. Therefore, the method for predicting the electrochemical lithium extraction electrode dissolution potential of the present invention ultimately chooses to use the steady-state diffusion coefficient and electrode dissolution potential at different lithium ion concentrations to fit the functional relationship. In Examples 4-11 below, the inventors respectively used lithium-containing solutions with lithium ion concentrations ranging from 15 mg / L to 2000 mg / L to confirm that the predicted values ​​obtained by the method for predicting the electrochemical lithium extraction electrode dissolution potential of the present invention, the test values ​​obtained by the device for predicting the electrochemical lithium extraction electrode dissolution potential of the present invention, and the consistency of the experimental test values, proved the feasibility of the method and device of the present invention.

[0093] Example 4

[0094] The activated lithium manganate electrode was used as the cathode, and the unactivated lithium manganate electrode was used as the anode. The cathode liquid was a lithium-containing solution with a lithium ion concentration of 15 mg / L and a pH of 7. The anode liquid was a 0.01M LiCl solution. A constant current of 50 mA was applied to the cathode liquid. When the electrode potential reached 0.68 V, the constant current was stopped, a constant potential of 0.68 V was applied to the cathode, and then the potential was reduced with a gradient of -0.02 V until electrode dissolution was observed, thereby obtaining the dissolution potential of the lithium manganate electrode at a lithium ion concentration of 15 mg / L, which was 0.58 V.

[0095] The activated lithium manganate electrode was used as the cathode, the titanium plate as the counter electrode, the KCl-saturated Ag / AgCl electrode as the reference electrode, and the cathode liquid was a lithium-containing solution with a lithium ion concentration of 15 mg / L. Constant current electrochemical impedance spectroscopy was performed at a frequency of 0.001 to 1*10 6 Hz, the current is 0.05 mA, and the steady-state diffusion coefficient of the lithium manganate electrode is 5.759*10 -6 cm 2 / s. Then, the functional relationship between the steady-state diffusion coefficient of the lithium manganate electrode and the electrode dissolution potential obtained in Example 1 was used to calculate the dissolution potential of the lithium manganate electrode at a lithium ion concentration of 15 mg / L, which was 0.578 V.

[0096] The device for predicting the dissolution potential of the electrochemical lithium extraction electrode of the present invention was used to test the dissolution potential of the lithium manganate electrode at a lithium ion concentration of 15 mg / L, and the dissolution potential was 0.583V.

[0097] It can be seen from the above results that at a lithium ion concentration of 15 mg / L, the dissolution potential of the lithium manganate electrode predicted by the method of the present invention and the dissolution potential of the lithium manganate electrode measured by the equipment of the present invention are basically consistent with the dissolution potential of the lithium manganate electrode measured experimentally.

[0098] Example 5

[0099] The steps of Example 4 were repeated, except that the lithium ion concentration of the lithium-containing solution was 30 mg / L, the constant potential applied to the cathode was 0.54 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA.

[0100] At a lithium ion concentration of 30 mg / L, the dissolution potential of the lithium manganate electrode predicted by the method of the present invention is 0.443 V, the dissolution potential of the lithium manganate electrode measured by the equipment of the present invention is 0.436 V, and the dissolution potential of the lithium manganate electrode measured experimentally is 0.44 V, and the three values ​​are basically consistent.

[0101] Example 6

[0102] The steps of Example 4 were repeated, except that the lithium ion concentration of the lithium-containing solution was 75 mg / L, the constant potential applied to the cathode was 0.44 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA.

[0103] At a lithium ion concentration of 75 mg / L, the dissolution potential of the lithium manganate electrode predicted by the method of the present invention is 0.343 V, the dissolution potential of the lithium manganate electrode measured by the equipment of the present invention is 0.338 V, and the dissolution potential of the lithium manganate electrode measured experimentally is 0.34 V, and the three values ​​are basically consistent.

[0104] Example 7

[0105] The steps of Example 4 were repeated, except that the lithium ion concentration of the lithium-containing solution was 500 mg / L, the constant potential applied to the cathode was 0.20 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA.

[0106] At a lithium ion concentration of 500 mg / L, the dissolution potential of the lithium manganate electrode predicted by the method of the present invention is 0.116 V, the dissolution potential of the lithium manganate electrode measured by the equipment of the present invention is 0.126 V, and the dissolution potential of the lithium manganate electrode measured experimentally is 0.12 V, and the three values ​​are basically consistent.

[0107] Example 8

[0108] The activated lithium iron phosphate electrode was used as the cathode and the unactivated lithium iron phosphate electrode as the anode. The cathode liquid was a lithium-containing solution with a lithium ion concentration of 15 mg / L and a pH of 5. The anode liquid was a 0.5M LiBr solution. A constant current of 1 mA was applied to the cathode liquid. When the electrode potential reached 0.76 V, the constant current was stopped, a constant potential of 0.76 V was applied to the cathode, and then the potential was reduced with a gradient of -0.02 V until electrode dissolution was observed, thereby obtaining the dissolution potential of the lithium manganate electrode at a lithium ion concentration of 15 mg / L, which was 0.66 V.

[0109] The activated lithium iron phosphate electrode was used as the cathode, the titanium plate as the counter electrode, the KCl-saturated Ag / AgCl electrode as the reference electrode, and the cathode liquid was a lithium-containing solution with a lithium ion concentration of 15 mg / L. Constant current electrochemical impedance spectroscopy was performed at a frequency of 0.001 to 1*10 6 Hz, the current is 0.05 mA, and the steady-state diffusion coefficient of the lithium iron phosphate electrode is 6.924*10 -6 cm 2 / s. Then, the functional relationship between the steady-state diffusion coefficient of the lithium iron phosphate electrode and the electrode dissolution potential obtained in Example 1 was used to calculate the dissolution potential of the lithium iron phosphate electrode at a lithium ion concentration of 15 mg / L, which was 0.664 V.

[0110] The device for predicting the dissolution potential of an electrochemical lithium extraction electrode of the present invention was used to test the dissolution potential of a lithium iron phosphate electrode at a lithium ion concentration of 15 mg / L, and the dissolution potential was 0.658 V.

[0111] It can be seen from the above results that at a lithium ion concentration of 15 mg / L, the dissolution potential of the lithium iron phosphate electrode predicted by the method of the present invention and the dissolution potential of the lithium iron phosphate electrode measured by the equipment of the present invention are basically consistent with the dissolution potential of the lithium iron phosphate electrode measured experimentally.

[0112] Example 9

[0113] The steps of Example 8 were repeated, except that the lithium ion concentration of the lithium-containing solution was 30 mg / L, the constant potential applied to the cathode was 0.64 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA. At a lithium ion concentration of 30mg / L, the dissolution potential of the lithium iron phosphate electrode predicted by the method of the present invention is 0.538V, the dissolution potential of the lithium iron phosphate electrode measured by the device of the present invention is 0.542V, and the dissolution potential of the lithium iron phosphate electrode measured experimentally is 0.54V, and the three values ​​are basically consistent.

[0114] Example 10

[0115] The steps of Example 8 were repeated, except that the lithium ion concentration of the lithium-containing solution was 75 mg / L, the constant potential applied to the cathode was 0.54 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA.

[0116] At a lithium ion concentration of 75 mg / L, the dissolution potential of the lithium iron phosphate electrode predicted by the method of the present invention is 0.442 V, the dissolution potential of the lithium iron phosphate electrode measured by the equipment of the present invention is 0.437 V, and the experimentally measured dissolution potential of the lithium iron phosphate electrode is 0.44 V, and the three values ​​are basically consistent.

[0117] Embodiment 11

[0118] The steps of Example 8 were repeated, except that the lithium ion concentration of the lithium-containing solution was 1000 mg / L, the constant potential applied to the cathode was -0.1 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA.

[0119] At a lithium ion concentration of 1000 mg / L, the dissolution potential of the lithium iron phosphate electrode predicted by the method of the present invention is -0.194 V, the dissolution potential of the lithium iron phosphate electrode measured by the equipment of the present invention is -0.206 V, and the experimentally measured dissolution potential of the lithium iron phosphate electrode is -0.20 V, and the three values ​​are basically consistent.

[0120] Example 12

[0121] The activated lithium titanate electrode was used as the cathode and the unactivated lithium titanate electrode as the anode. The cathode liquid was a lithium-containing solution with a lithium ion concentration of 15 mg / L and a pH of 5. The anode liquid was a 1M Li2C2O4 solution. A constant current of 25 mA was applied to the cathode liquid. When the electrode potential reached 0.50 V, the constant current was stopped, a constant potential of 0.50 V was applied to the cathode, and then the potential was reduced with a gradient of -0.02 V until electrode dissolution was observed, thereby obtaining the dissolution potential of the lithium titanate electrode at a lithium ion concentration of 15 mg / L, which was 0.42 V.

[0122] The activated lithium titanate electrode was used as the cathode, the titanium plate as the counter electrode, the KCl-saturated Ag / AgCl electrode as the reference electrode, and the cathode liquid was a lithium-containing solution with a lithium ion concentration of 15 mg / L. Constant current electrochemical impedance spectroscopy was performed, 0.001~1*10 6 Hz, the current is 0.05 mA, and the steady-state diffusion coefficient of the lithium titanate electrode is 3.799*10 - 6 cm 2 / s. Then, the functional relationship between the steady-state diffusion coefficient of the lithium titanate electrode and the electrode dissolution potential obtained in Example 1 was used to calculate the dissolution potential of the lithium titanate electrode at a lithium ion concentration of 15 mg / L, which was 0.422 V.

[0123] The device for predicting the dissolution potential of an electrochemical lithium extraction electrode of the present invention was used to test the dissolution potential of a lithium titanate electrode at a lithium ion concentration of 75 mg / L, and the dissolution potential was 0.415 V.

[0124] It can be seen from the above results that at a lithium ion concentration of 15 mg / L, the dissolution potential of the lithium titanate electrode predicted by the method of the present invention and the dissolution potential of the lithium titanate electrode measured by the equipment of the present invention are basically consistent with the dissolution potential of the lithium titanate electrode measured experimentally.

[0125] Example 13

[0126] The steps of Example 12 were repeated except that the lithium ion concentration of the lithium-containing solution was 30 mg / L, the constant potential applied to the cathode was 0.32 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA.

[0127] At a lithium ion concentration of 30 mg / L, the dissolution potential of the lithium titanate electrode predicted by the method of the present invention is 0.221 V, the dissolution potential of the lithium titanate electrode measured by the equipment of the present invention is 0.228 V, and the dissolution potential of the lithium titanate electrode measured experimentally is 0.22 V, and the three values ​​are basically consistent.

[0128] Embodiment 14

[0129] The steps of Example 12 were repeated except that the lithium ion concentration of the lithium-containing solution was 75 mg / L, the constant potential applied to the cathode was 0.20 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*10 6 Hz, current is 0.05mA.

[0130] At a lithium ion concentration of 75 mg / L, the dissolution potential of the lithium titanate electrode predicted by the method of the present invention is 0.143 V, the dissolution potential of the lithium titanate electrode measured by the equipment of the present invention is 0.138 V, and the dissolution potential of the lithium titanate electrode measured experimentally is 0.14 V, and the three values ​​are basically consistent.

[0131] Embodiment 15

[0132] The steps of Example 12 were repeated, except that the lithium ion concentration of the lithium-containing solution was 2000 mg / L, the constant potential applied to the cathode was -0.8 V, and the frequency in the constant current electrochemical impedance spectroscopy test was 0.001 to 1*106 Hz, current is 0.05mA.

[0133] At a lithium ion concentration of 2000 mg / L, the dissolution potential of the lithium titanate electrode predicted by the method of the present invention is -0.924 V, the dissolution potential of the lithium titanate electrode measured by the equipment of the present invention is -0.916 V, and the dissolution potential of the lithium titanate electrode measured experimentally is -0.92 V, and the three values ​​are basically consistent.

[0134] The above-described embodiments are only specific implementation methods of the present invention, which are used to illustrate and explain the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited to the given embodiments, but should be based on the protection scope of the claims of the present invention. At the same time, it should be understood by ordinary technicians in this field that any technician familiar with the technical field can still modify, change or replace the technical solutions recorded in the embodiments of the present invention within the technical scope disclosed by the present invention. These modifications, changes or equivalent replacements do not deviate from the spirit and essence of the technical solutions of the embodiments of the present invention, and should be covered within the protection scope of the present invention.

Claims

1. A method for predicting the electrochemical lithium extraction electrode dissolution potential, comprising the following steps: Step S1: Obtaining the steady-state diffusion coefficient of the lithium-extracting electrode at different lithium ion concentrations The steady-state diffusion coefficient of the lithium-extracting electrode at different lithium ion concentrations was obtained by constant current electrochemical impedance spectroscopy (EIS) test. The operating conditions were: frequency range 0.001~1*10 6 Hz, current is less than 1mA; Step S2: Obtaining the dissolution potential of the lithium-extracting electrode at different lithium ion concentrations The unactivated lithium extraction electrode is used as the anode and the lithium extraction electrode activated by electrochemical oxidation is used as the cathode, the cathode is provided with a reference electrode, the cathode liquid is a lithium-containing solution, and the anode liquid is a lithium-containing conductive solution; S2-1: Obtain the estimated range of lithium extraction electrode dissolution potential A constant current is applied to the cathode liquid, and a point test is performed during the process of potential reduction until electrode dissolution occurs. The experiment is repeated at different lithium ion concentrations to obtain the estimated range of potential loss of the lithium extraction electrode at different concentrations. S2-2: Obtain the accurate value of the lithium extraction electrode dissolution potential A constant current is applied to the cathode liquid. When the electrode potential reaches a set value within the estimated range of the dissolution potential of the lithium extraction electrode, a constant potential is applied to the lithium extraction electrode to observe whether dissolution occurs. If not, the applied constant potential is changed in a gradient until electrode dissolution is observed. The experiment is repeated at different lithium ion concentrations to obtain accurate dissolution potentials at different lithium ion concentrations. Step S3: Establishing the functional relationship between the lithium extraction electrode dissolution potential and the steady-state diffusion coefficient Based on the steady-state diffusion coefficient obtained in step S1 and the dissolution potential obtained in step S2, a functional relationship between the dissolution potential and the diffusion coefficient of the lithium extraction electrode under different lithium ion concentrations is obtained by fitting; Step S4: Real-time prediction of the dissolution potential of the lithium extraction electrode During the electrochemical lithium extraction process, the steady-state diffusion coefficient of the lithium extraction electrode is measured in real time, and the dissolution potential of the lithium extraction electrode is calculated in real time according to the functional relationship between the dissolution potential of the lithium extraction electrode and the diffusion coefficient obtained in step S3.

2. The method for predicting the dissolution potential of an electrochemical lithium extraction electrode according to claim 1, wherein the lithium extraction electrode is a lithium manganate electrode, a lithium iron phosphate electrode or a lithium titanate electrode.

3. The method for predicting the electrochemical lithium extraction electrode dissolution potential according to claim 1, wherein the anolyte is a lithium chloride, lithium bromide, lithium fluoride, lithium nitrate, lithium acetate, lithium oxalate, lithium sulfate, lithium acetate or lithium formate solution with a concentration of 0.01-1M.

4. The method for predicting the electrochemical lithium extraction electrode dissolution potential according to claim 1, wherein the lithium ion concentration in the lithium-containing solution is 0-2000 mg / L.

5. The method for predicting the dissolution potential of an electrochemical lithium extraction electrode according to claim 1, wherein in the constant current electrochemical impedance spectroscopy test in step S1, the cathode is a lithium extraction electrode after electrochemical oxidation activation, and the cathode liquid is a lithium-containing solution.

6. The method for predicting the dissolution potential of an electrochemical lithium extraction electrode according to claim 5, wherein the electrode substrate material is one or more of a graphite sheet, a titanium sheet, a carbon cloth, a carbon felt, a platinum sheet, a gold sheet, a silver sheet, a copper sheet, and an aluminum sheet.

7. The method for predicting the electrochemical lithium extraction electrode dissolution potential according to claim 1, wherein the constant current range described in step S2 is 1-50 mA.

8. The method for predicting the dissolution potential of an electrochemical lithium extraction electrode according to claim 1, wherein the potential value is tested at a point with a gradient of ≤-0.1V in step S2-1.

9. The method for predicting the dissolution potential of an electrochemical lithium extraction electrode according to claim 1, wherein in step S2-2, a constant potential is applied to the lithium extraction electrode with a gradient change of ≤-0.02V.

10. An apparatus for predicting the dissolution potential of an electrochemical lithium extraction electrode, comprising: an electrode set, which consists of a working electrode, a counter electrode and a reference electrode; EIS real-time monitor, used to measure the steady-state diffusion coefficient of the working electrode in real time; A data analyzer storing therein a functional relationship between the electrode dissolution potential and the diffusion coefficient obtained according to the method of claims 1 to 9, for real-time calculation of the dissolution potential of the working electrode; The electrode potential responder is used to adjust the potential of the working electrode in real time according to the calculation results of the data analyzer.

11. The device for predicting the dissolution potential of an electrochemical lithium extraction electrode according to claim 10, wherein the working electrode is a lithium manganate electrode, a lithium iron phosphate electrode or a lithium titanate electrode.

12. Application of equipment for predicting the dissolution potential of electrochemical lithium extraction electrodes in the extraction of lithium from lithium-containing solutions.

Images