Characterization method for transference number of lithium ions in lithium ion electrolyte

Abstract

The invention discloses a characterization method for the transference number of lithium ions in a lithium ion electrolyte, and relates to the technical field of lithium batteries, and the method comprises the following steps: firstly, preparing aluminum lithium alloy powder into slurry, coating the surface of an aluminum foil with the slurry, drying, and cutting to prepare an aluminum lithium pole piece; sequentially placing an aluminum-lithium pole piece, a diaphragm and an aluminum-lithium pole piece on a pole piece fixing table, and dropwise adding electrolyte before and after placing a layer of diaphragm every time; then a circular sealing ring is placed, a sealing ring is pressed down, and a positive electrode pressing ring is covered and is tightened and fixed through a stud; connecting the two ends of the assembled device through an electrode lead to enable the device to be short-circuited, and standing for 6 hours to enable the open-circuit voltage of the device to be balanced to 0V; an electrochemical workstation is used for testing the alternating-current impedance spectrum of the device, and a pre-polarization impedance diagram of the device is obtained; according to the method, the lithium ion transference number of the electrolyte can be simply and quickly analyzed, the performance difference of the lithium ion transmission efficiency of the electrolyte with different formulas can be accurately reflected, and a basis is provided for formula optimization of the electrolyte.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically a method for characterizing the lithium ion transport number in a lithium-ion electrolyte. Background Technology

[0002] With the increasing popularity of electric vehicles and portable electronic devices, consumers have increasingly higher demands for battery performance, especially for charging speed. Lithium-ion batteries, as the core of modern high-rate battery devices, rely heavily on the lithium-ion transport efficiency in the electrolyte. The transport speed of lithium ions in the electrolyte not only determines the battery's charge and discharge rate but also directly affects its energy density, rate performance, cycle stability, and safety. Specifically, one of the key indicators of lithium-ion transport performance—the lithium-ion transference number—reflects the proportion of lithium ions contributing to the total current and has a decisive impact on the overall battery performance.

[0003] Currently, the charging speed of lithium-ion batteries is limited by the kinetics of lithium-ion insertion and extraction, while high-rate batteries achieve fast charging by optimizing electrode materials and electrolytes.

[0004] However, a low lithium-ion transference number in the electrolyte can exacerbate polarization in the battery under high current or low temperature conditions, leading to capacity decay and energy loss. This is particularly true in the electric vehicle sector, where fast-charging technology requires electrolytes with high ionic conductivity and high lithium-ion transference numbers to reduce concentration polarization and improve charging efficiency.

[0005] Currently, the main methods for testing the lithium-ion migration performance in lithium-ion battery electrolytes include pulsed field gradient nuclear magnetic resonance (PMR), electrophoretic NMR, and the Bruce-Vincent method. However, these methods all have limitations to varying degrees: Pulsed-field gradient nuclear magnetic resonance (PMR): This technique measures the self-diffusion coefficient of molecules or ions by detecting the displacement of particles through the application of a gradient magnetic field. However, it only reflects the self-diffusion behavior of the electrolyte and may differ from the actual electrochemical transport number. Furthermore, the equipment is expensive, requires isotope labeling, and is complex to operate, making it difficult to widely apply in industrial production.

[0006] Electrophoretic NMR: This technique combines electrophoresis and NMR to directly measure the electromobility and transport number of ions in an electrolyte. However, it has a weak signal for low-concentration ions and may trigger side reactions in the electrolyte. Furthermore, the equipment is complex, requiring customized electrodes and electric field control systems, further limiting its application.

[0007] Bruce-Vincent method: This method uses coin cells to assemble symmetrical cells (lithium-electrolyte-lithium). A small DC voltage is applied, and the initial and steady-state currents are measured. The transference number is calculated by combining the bulk resistance and steady-state resistance measured using AC impedance. However, interfacial side reactions can occur between lithium metal and the electrolyte, leading to short circuits or uneven local current densities, thus affecting the accuracy of the steady-state current measurement. Summary of the Invention

[0008] The purpose of this invention is to provide a method for characterizing the lithium ion transference number in a lithium-ion electrolyte, so as to solve the problems in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for characterizing the lithium-ion transport number in a lithium-ion electrolyte includes the following steps: Step 1: Prepare aluminum-lithium alloy powder into a slurry, coat it onto the surface of aluminum foil, dry it, and then cut it into aluminum-lithium electrode sheets; Step 2: Place aluminum-lithium electrodes, separators, and aluminum-lithium electrodes in sequence on the electrode fixing platform. Electrolyte needs to be added before and after each layer of separator is placed. Step 3: Then place the round sealing ring, press down the sealing ring, cover the positive electrode pressure ring, and tighten it with the studs; Step 4: Connect the assembled device through the two ends of the electrode leads to short-circuit it, and let it stand for 6 hours to allow the open-circuit voltage of the device to balance to 0V. Step 5: Use an electrochemical workstation to test the AC impedance spectrum of the device to obtain the impedance diagram of the device before polarization; Step 6: Using the i~t function in the electrochemical workstation, apply a 10mV voltage to the device for constant potential polarization for 2 hours, and record the maximum current value at the beginning of the device as the initial current I0, and the current value after the i~t curve of the device stabilizes as the steady-state current Is. Step 7: After the device is polarized, the AC impedance spectrum of the device is tested again using an electrochemical workstation to obtain the impedance diagram of the device after polarization. Step 8: Calculate the lithium-ion transference number based on the impedance spectrum and the initial and steady-state current values.

[0010] Based on the above technical solutions, the present invention also provides the following optional technical solutions: In one alternative: in step two, the electrolyte is a lithium hexafluorophosphate solution.

[0011] In one alternative: the lithium hexafluorophosphate solution is based on a mixed solution of ethylene carbonate and dimethyl carbonate.

[0012] In one alternative: the circular sealing ring is made of high-sealing rubber or plastic to ensure the sealing effect of the entire device, prevent electrolyte leakage, and improve the stability of the battery.

[0013] In one alternative: the device includes a compression spring for filling the entire battery, ensuring good contact between the electrode plates and the battery, thereby guaranteeing the stability and accuracy of the test.

[0014] In one alternative: In step four, the device is allowed to rest with a short circuit to balance its open-circuit voltage to 0V, ensuring the consistency of the initial test conditions and improving the accuracy of the test.

[0015] In one alternative: in steps five and seven, the AC voltage disturbance parameter of the electrochemical workstation is set to 10mV, and the impedance frequency test range is 100kHz to 0.01Hz.

[0016] In one alternative: in step seven, the , ; in, For the initial current, For steady-state current, and These are the test values ​​before and after polarization, respectively.

[0017] In one alternative: In step eight, the formula for calculating the lithium-ion transport number is: .

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention can quickly and easily analyze the lithium-ion transference number of electrolytes, accurately reflect the differences in lithium-ion transport efficiency performance of electrolytes with different formulations, and provide a basis for electrolyte formulation optimization.

[0019] 2. The device used in this invention is designed with ease of use and stability in mind. For example, it uses highly sealing materials to prevent electrolyte leakage and integrates compression springs to ensure good contact between the electrode plates and the battery. These designs improve the efficiency and accuracy of the test, have low requirements, are simple to operate, and have high test accuracy, with stable and reliable test results. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the device of the present invention.

[0021] Figure 2 This is a timing current curve diagram of the present invention.

[0022] Figure 3 The diagram shows the impedance curves of the device before and after polarization.

[0023] Figure 4 This is a charge-discharge curve of the electrolyte with different lithium salt concentrations according to the present invention.

[0024] Figure label annotations: 1. Electrode lead; 2. Positive electrode pressure ring; 3. Compression spring; 4. Sealing ring; 5. Circular sealing ring; 6. Electrode fixing platform; 7. Negative electrode support platform; 8. Stud. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] In one embodiment, such as Figures 1-4 As shown, a method for characterizing the lithium-ion transport number in a lithium-ion electrolyte includes the following steps: Step 1: Prepare aluminum-lithium alloy powder into a slurry, coat it onto the surface of aluminum foil, dry it, and then cut it into aluminum-lithium electrode sheets; Step 2: Place aluminum-lithium electrode, separator, and aluminum-lithium electrode in sequence on the electrode fixing platform 6. Electrolyte needs to be added before and after each layer of separator is placed. Step 3: Then place the round sealing ring 5, press down the sealing ring 4, cover the positive electrode pressure ring 2, and tighten it with the stud 8; Step 4: Connect the assembled device through the two ends of electrode lead 1 to short-circuit it, and let it stand for 6 hours to allow the open-circuit voltage of the device to balance to 0V. Step 5: Use an electrochemical workstation to test the AC impedance spectrum of the device to obtain the impedance diagram of the device before polarization; Step 6: Using the i~t function in the electrochemical workstation, apply a 10mV voltage to the device for constant potential polarization for 2 hours, and record the maximum current value at the beginning of the device as the initial current I0, and the current value after the i~t curve of the device stabilizes as the steady-state current Is. Step 7: After the device is polarized, the AC impedance spectrum of the device is tested again using an electrochemical workstation to obtain the impedance diagram of the device after polarization. Step 8: Calculate the lithium-ion transference number based on the impedance spectrum and the initial and steady-state current values.

[0027] In this embodiment, in step two, an appropriate amount of electrolyte needs to be added before and after each layer of diaphragm is placed to ensure that the electrolyte fully wets the electrode and diaphragm and promotes ion conduction.

[0028] In step three, a circular sealing ring 5 is placed on the assembled battery structure to prevent electrolyte leakage; the sealing ring 4 is pressed down, the positive electrode pressure ring 2 is covered, and the entire device is tightened and fixed by the stud 8 to ensure the stability and sealing of the battery structure.

[0029] The purpose of step four is to balance the open-circuit voltage of the device to 0V, ensuring the consistency of the initial test conditions and thus improving the accuracy of the test.

[0030] Step five helps to understand the electrochemical performance of the battery in its initial state.

[0031] In step six, the maximum current value at the start of the device is recorded as the initial current I0, and the current value after the i~t curve of the device stabilizes is recorded as the steady-state current Is. These data are crucial for the subsequent calculation of the lithium-ion transference number.

[0032] In step seven, by comparing the impedance changes before and after polarization, the migration behavior of lithium ions in the electrolyte can be further analyzed.

[0033] In step eight, the lithium-ion transference number is calculated using a specific formula. This step is the core of the entire characterization method, as it directly reflects the lithium-ion transport efficiency in the electrolyte.

[0034] In one embodiment, in step two, the electrolyte is a lithium hexafluorophosphate solution.

[0035] The lithium hexafluorophosphate solution is based on a mixed solution of ethylene carbonate and dimethyl carbonate.

[0036] It should be noted that by specifying that the electrolyte is a lithium hexafluorophosphate solution and using its mixed solvent system as a base, the method in this embodiment significantly improves the accuracy and reliability of lithium-ion transport number testing while maintaining ease of operation, which is of great significance for promoting the development of lithium-ion battery technology.

[0037] In one embodiment, the circular sealing ring 5 is made of high-sealing rubber or plastic to ensure the sealing effect of the entire device, prevent electrolyte leakage, and improve the stability of the battery.

[0038] It should be noted that high-sealing rubber or plastic is explicitly used as the material for the circular sealing ring 5. These materials possess excellent elasticity, chemical resistance, and sealing performance, effectively adapting to pressure changes during battery assembly and maintaining a sealed state over a long period.

[0039] The circular sealing ring 5 forms a sealing barrier through physical compression, effectively blocking the electrolyte from seeping out from the gap between the electrode fixing platform 6 and the sealing ring 4, thus avoiding problems such as battery capacity decay and increased self-discharge caused by leakage.

[0040] In one embodiment, the device includes a compression spring 3 for filling the entire battery, ensuring good contact between the electrode plates and the battery, thereby guaranteeing the stability and accuracy of the test.

[0041] It should be noted that the compression spring 3 is integrated inside the battery device. Its core function is to fill the gap between the electrode sheet and the battery casing through elastic deformation, while providing a continuous and uniform preload. This design ensures tight contact between the electrode sheet (such as the aluminum lithium electrode sheet) and components such as the current collector and separator, avoiding poor contact caused by assembly tolerances or material deformation.

[0042] The introduction of compression spring 3 solves the performance degradation problem caused by mechanical relaxation in traditional battery devices, and is especially suitable for scenarios requiring long-term stable testing or dynamic operating conditions (such as lithium-ion transference number characterization). Its low cost and easy integration make it widely applicable in the fields of battery R&D and quality inspection.

[0043] In one embodiment, in step four, the device balances its open-circuit voltage to 0V by short-circuiting and allowing it to stand still, ensuring the consistency of the initial test conditions and improving the accuracy of the test.

[0044] It should be noted that short-circuit static setting forces all test devices to start from the same electrochemical baseline (OCV=0V), eliminating the initial potential dispersion caused by assembly differences (such as electrode thickness, electrolyte distribution) or environmental factors (temperature fluctuations).

[0045] By achieving precise zeroing of the open-circuit voltage through short-circuit resting, the variable of the initial test conditions is eliminated from the source, laying the foundation for high-precision characterization of lithium-ion transference numbers.

[0046] In one embodiment, in steps five and seven, the AC voltage disturbance parameter of the electrochemical workstation is set to 10mV, and the impedance frequency test range is 100kHz to 0.01Hz.

[0047] It should be noted that the 10mV perturbation amplitude has been experimentally verified to be the optimal value for balancing sensitivity and linearity: it can excite a measurable current response without causing significant changes to the double-layer structure or charge transfer reaction on the electrode surface. The range of 100kHz to 0.01Hz covers all key frequency bands for lithium-ion battery EIS testing, while logarithmic interval sampling keeps the single test time within 5 minutes, balancing data density and experimental efficiency.

[0048] By combining a 10mV AC voltage disturbance with an impedance frequency range of 100kHz-0.01Hz, and through a scientific balance of sensitivity, linearity, and testing efficiency, high-precision, full-frequency characterization of the electrochemical impedance of lithium-ion batteries is achieved.

[0049] In one embodiment, in step seven, the , ; in, For the initial current, For steady-state current, and These are the test values ​​before and after polarization, respectively.

[0050] In step eight, the formula for calculating the lithium-ion transport number is: .

[0051] It should be noted that the above calculation formula is based on electrochemical polarization theory, quantifying the contribution of ion migration through a current-impedance correlation model. (Numerator term) Correcting the "effective migration component" of the initial current affected by impedance, the denominator term This corrects the "actual migration component" of the steady-state current affected by the impedance after polarization, and the final ratio reflects the proportion of lithium ions in the total ion migration.

[0052] By quantifying the lithium-ion transference number, it directly correlates electrolyte formulation optimization (such as solvent ratio and additive selection) with battery rate performance improvement, providing crucial data support for the development of high-rate batteries. Its "simple operation and stable results" significantly lower the technical barrier, making it suitable for rapid screening and quality control in large-scale production.

[0053] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0054] Example 1 The lithium salt concentration of the lithium hexafluorophosphate electrolyte is 0.3 mol / L.

[0055] Preparation steps for 0.3 mol / L electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), weigh 4.557 g of lithium hexafluorophosphate and transfer it to a 100 mL volumetric flask.

[0056] Add 40-50 mL of mixed solvent (ethylene carbonate: dimethyl carbonate = 1:1 volume ratio), shake gently until LiPF6 is completely dissolved, and after the solution is cooled to room temperature, add the remaining solvent dropwise to the mark of the volumetric flask.

[0057] Invert the volumetric flask 20 times to ensure the solution is completely homogeneous before testing.

[0058] See the attached diagram in the instruction manual for details. Figure 2 , Figure 3 The electrolyte was subjected to the characterization method for lithium-ion transport number in the aforementioned lithium-ion electrolyte. The chronoamperometry curve and electrochemical impedance spectroscopy of the electrolytic cell were tested, and relevant parameters were obtained. For the initial current, For steady-state current, and These are the test values ​​before and after polarization, respectively.

[0059] According to the formula for calculating the lithium-ion transport number: ;in, , .

[0060] Example 2 The lithium salt concentration of the lithium hexafluorophosphate electrolyte is 0.6 mol / L.

[0061] Preparation steps for 0.6 mol / L electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), weigh 9.115 g of lithium hexafluorophosphate and transfer it to a 100 mL volumetric flask.

[0062] Add 40-50 mL of mixed solvent (ethylene carbonate: dimethyl carbonate = 1:1 volume ratio), shake gently until LiPF6 is completely dissolved, and after the solution is cooled to room temperature, add the remaining solvent dropwise to the mark of the volumetric flask.

[0063] Invert the volumetric flask 20 times to ensure the solution is completely homogeneous before testing.

[0064] See the attached diagram in the instruction manual for details. Figure 2 , Figure 3 The electrolyte was subjected to the characterization method for lithium-ion transport number in the aforementioned lithium-ion electrolyte. The chronoamperometry curve and electrochemical impedance spectroscopy of the electrolytic cell were tested, and relevant parameters were obtained. For the initial current, For steady-state current, and These are the test values ​​before and after polarization, respectively.

[0065] According to the formula for calculating the lithium-ion transport number: ;in, , .

[0066] Example 3 The lithium salt concentration of the lithium hexafluorophosphate electrolyte is 0.9 mol / L.

[0067] Preparation steps for 0.9 mol / L electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), weigh 13.672 g of lithium hexafluorophosphate and transfer it to a 100 mL volumetric flask.

[0068] Add 40-50 mL of mixed solvent (ethylene carbonate: dimethyl carbonate = 1:1 volume ratio), shake gently until LiPF6 is completely dissolved, and after the solution is cooled to room temperature, add the remaining solvent dropwise to the mark of the volumetric flask.

[0069] Invert the volumetric flask 20 times to ensure the solution is completely homogeneous before testing.

[0070] See the attached diagram in the instruction manual for details. Figure 2 , Figure 3 The electrolyte was subjected to the characterization method for lithium-ion transport number in the aforementioned lithium-ion electrolyte. The chronoamperometry curve and electrochemical impedance spectroscopy of the electrolytic cell were tested, and relevant parameters were obtained. For the initial current, For steady-state current, and These are the test values ​​before and after polarization, respectively.

[0071] According to the formula for calculating the lithium-ion transport number: ;in, , .

[0072] Example 4 The lithium salt concentration of the lithium hexafluorophosphate electrolyte is 1.2 mol / L.

[0073] Preparation steps for 1.2 mol / L electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), weigh 18.229 g of lithium hexafluorophosphate and transfer it to a 100 mL volumetric flask.

[0074] Add 40-50 mL of mixed solvent (ethylene carbonate: dimethyl carbonate = 1:1 volume ratio), shake gently until LiPF6 is completely dissolved, and after the solution is cooled to room temperature, add the remaining solvent dropwise to the mark of the volumetric flask.

[0075] Invert the volumetric flask 20 times to ensure the solution is completely homogeneous before testing.

[0076] See the attached diagram in the instruction manual for details. Figure 2 , Figure 3 The electrolyte was subjected to the characterization method for lithium-ion transport number in the aforementioned lithium-ion electrolyte. The chronoamperometry curve and electrochemical impedance spectroscopy of the electrolytic cell were tested, and relevant parameters were obtained. For the initial current, For steady-state current, and These are the test values ​​before and after polarization, respectively.

[0077] According to the formula for calculating the lithium-ion transport number: ;in, , .

[0078] Example 5 The lithium salt concentration of the lithium hexafluorophosphate electrolyte is 1.5 mol / L.

[0079] Preparation steps for 1.5 mol / L electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), weigh 22.787 g of lithium hexafluorophosphate and transfer it to a 100 mL volumetric flask.

[0080] Add 40-50 mL of mixed solvent (ethylene carbonate: dimethyl carbonate = 1:1 volume ratio), shake gently until LiPF6 is completely dissolved, and after the solution is cooled to room temperature, add the remaining solvent dropwise to the mark of the volumetric flask.

[0081] Invert the volumetric flask 20 times to ensure the solution is completely homogeneous before testing.

[0082] See the attached diagram in the instruction manual for details. Figure 2 , Figure 3 The electrolyte was subjected to the characterization method for lithium-ion transport number in the aforementioned lithium-ion electrolyte. The chronoamperometry curve and electrochemical impedance spectroscopy of the electrolytic cell were tested, and relevant parameters were obtained. For the initial current, For steady-state current, and These are the test values ​​before and after polarization, respectively.

[0083] According to the formula for calculating the lithium-ion transport number: ;in, , .

[0084] All five embodiments described above underwent two tests, and the test results are shown in the following table of lithium ion transport numbers at different lithium salt concentrations and the accompanying drawings. Figure 4 As shown.

[0085] Table of lithium ion transport numbers at different lithium salt concentrations:

[0086] Combined with the lithium-ion transport number table for different lithium salt concentrations and the accompanying diagram in the instruction manual. Figure 4 The following conclusions can be drawn: As the lithium salt concentration increased from 0.3 mol / L to 1.5 mol / L, the lithium-ion transport number increased from 0.1676 to 0.4347. The charge-discharge curves showed the same trend: with increasing lithium salt concentration, the charge-discharge capacity increased, and the battery polarization decreased, indicating an increase in lithium-ion migration rate. This demonstrates that the current testing method has good recognition accuracy for lithium salt concentration and can accurately reflect the differences in lithium-ion transport efficiency performance of electrolytes with different formulations.

[0087] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for characterizing the number of lithium ions transferred in a lithium-ion electrolyte, characterized in that, The method comprises the following steps: Step 1: The aluminum-lithium alloy powder is made into a slurry, coated on the surface of an aluminum foil, dried, and cut into an aluminum-lithium electrode sheet; Step 2: The aluminum-lithium electrode sheet, a separator, and the aluminum-lithium electrode sheet are sequentially placed on the electrode sheet fixing table (6), and electrolyte is added before and after each layer of the separator is placed; Step 3: A round sealing ring (5) is then placed, the sealing ring (4) is pressed down, the positive electrode compression ring (2) is covered, and is fixed by screwing the stud (8); Step 4: The assembled device is connected by the electrode lead (1) at both ends to make it short-circuit, and is placed for 6 hours, so that the open-circuit voltage of the device is balanced to 0V; Step 5: The electrochemical workstation is used to test the alternating current impedance spectrum of the device, and the impedance diagram of the device before polarization is obtained; Step 6: The i~t function in the electrochemical workstation is used to apply a 10mV voltage to the device for 2 hours, and the maximum current value at the beginning of the device is recorded as the initial current I0, and the current value after the i~t curve of the device is stabilized is recorded as the steady-state current Is; Step 7: After the polarization of the device, the electrochemical workstation is used to test the alternating current impedance spectrum of the device again, and the impedance diagram of the device after polarization is obtained; Step 8: The lithium ion transfer number is calculated according to the impedance spectrum diagram and the initial and steady-state current values.

2. The method of claim 1, wherein the number of lithium ions transferred in the lithium-ion electrolyte is represented by the formula: ###0001### wherein: n is the number of lithium ions transferred; m is the number of electrons transferred; and A is the Faraday constant. In step 2, the electrolyte is a lithium hexafluorophosphate solution.

3. The method of claim 2, wherein the number of lithium ions transferred in the lithium-ion electrolyte is represented by the formula: ###0001### wherein: n is the number of lithium ions transferred; m is the number of electrons transferred; and A is the Faraday constant. The lithium hexafluorophosphate solution is based on a mixed solution of ethylene carbonate and dimethyl carbonate.

4. The method for characterizing the lithium-ion transference number in a lithium-ion electrolyte according to claim 1, characterized in that, The material of the round sealing ring (5) is high-sealing rubber or plastic.

5. The method of claim 1, wherein the number of lithium ions transferred in the lithium-ion electrolyte is represented by the following equation: ###0001### wherein, n is the number of lithium ions transferred in the lithium-ion electrolyte; F is the Faraday constant; Q is the charge of the lithium ion; and I is the current. The device comprises a compression spring (3).

6. The method of claim 1, wherein the number of lithium ions transferred in the lithium-ion electrolyte is represented by the following equation: ###0001### wherein, n is the number of lithium ions transferred in the lithium-ion electrolyte; F is the Faraday constant; Q is the charge of the lithium ion; and I is the current. In step 4, the device is placed by short-circuit to balance the open-circuit voltage of the device to 0V.

7. The method of claim 1, wherein the number of lithium ions transferred in the lithium-ion electrolyte is represented by the following equation: ###0001### wherein, n is the number of lithium ions transferred in the lithium-ion electrolyte; F is the Faraday constant; Q is the charge of the lithium ion; and I is the current. In steps 5 and 7, the electrochemical workstation alternating voltage disturbance parameter is set to 10mV, and the impedance frequency test range is 100kHz to 0.01Hz.

8. The method of claim 1, wherein the number of lithium ions transferred in the lithium-ion electrolyte is characterized by, In step seven, the , ; wherein, is the initial current, is the steady state current, and are the test values before and after polarization, respectively.

9. The method of claim 1, wherein the number of lithium ions transferred in the lithium-ion electrolyte is characterized by, In step eight, the formula for calculating the number of lithium ions migrated is: .

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