Method for testing diffusion coefficient of lithium ions in lithium ion battery and application

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a method for testing the diffusion coefficient of lithium ions in a lithium ion battery and application. The method comprises the following steps: firstly, assembling a lithium ion three-electrode battery, and carrying out lithium plating treatment on a reference electrode of the lithium ion three-electrode battery by using current to obtain a lithium-plated lithium ion three-electrode battery; measuring impedance data of a total battery, a positive electrode / reference electrode and a negative electrode / reference battery in the lithium ion three-electrode battery plated with lithium by adopting an in-situ electrochemical impedance method, and setting a voltage disturbance value to be 5-10mV and the frequency to be 0.01-105Hz; and finally, processing the impedance data, obtaining a corresponding Warburg coefficient sigma through the impedance data, and calculating the lithium ion diffusion coefficient through the following formula. According to the invention, the diffusion coefficient of the lithium ion total battery can be rapidly obtained, the test method is simple, and the test period is short.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and particularly relates to a method for testing the lithium-ion diffusion coefficient in lithium-ion batteries and its application. Background Technology

[0002] The positive and negative electrode materials of lithium-ion batteries are mostly layered compounds capable of lithium ion insertion and extraction. During charging and discharging, the solid-phase diffusion process of lithium insertion / extraction is a slow process and often becomes the controlling step. The diffusion coefficient of the diffusion process determines the reaction rate. The larger the diffusion coefficient, the better the high-current discharge capability of the electrode, the higher the power density of the material, and the better the high-rate performance. Therefore, measuring the diffusion coefficient of lithium ions in positive and negative electrode materials is of great significance.

[0003] Currently, common methods for testing lithium-ion diffusion coefficients include PITT, GITT, LSV, and NMR. PITT is only suitable for materials with a distinct potential plateau, limiting its applicability to materials without a clear plateau, and its current signal is easily affected by interfacial impedance and side reactions. GITT has a long testing cycle (single pulse takes several hours), making it unsuitable for high-throughput screening. It also requires accurate measurement of electrode thickness and active material content, placing high demands on sample preparation; it relies on ideal polarization conditions, which may be affected by ohmic impedance in practical applications. LSV has drawbacks such as concentration polarization potentially masking the true diffusion behavior at high scan rates. NMR requires superconducting magnets, making the equipment expensive and complex to operate, requiring specialized personnel. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a method and application for testing the lithium-ion diffusion coefficient in lithium-ion batteries. This invention has advantages such as simple method, short testing cycle, and applicability to large battery cells.

[0005] To achieve one of the above objectives, the present invention adopts the following technical solution:

[0006] A method for testing the lithium-ion diffusion coefficient in a lithium-ion battery, the specific steps of which are as follows:

[0007] S1. Assemble a lithium-ion three-electrode battery and use current to plate lithium on the reference electrode of the lithium-ion three-electrode battery to obtain a lithium-plated lithium-ion three-electrode battery.

[0008] S2. The impedance data of the full cell, positive electrode / reference electrode, and negative electrode / reference cell in the lithium-ion three-electrode battery after lithium plating are measured using the in-situ electrochemical impedance spectroscopy method. The voltage perturbation value is set to 5-10mV, and the frequency is 0.01Hz-10Hz. 5 Hz;

[0009] S3. Process the impedance data to obtain the corresponding Warburg coefficient σ, and calculate the lithium-ion diffusion coefficient using the following formula:

[0010]

[0011] In the formula:

[0012] D Li+ —The diffusion coefficient of lithium ions in battery materials, expressed in square centimeters per second (cm²). 2 / s);

[0013] R—ideal gas constant, 8.314 J / (mol·K);

[0014] T – Test temperature, in Kelvin (K);

[0015] n—the number of electrons transferred in a chemical reaction;

[0016] F—Faraday constant, 96500 C / mol;

[0017] A – Area of ​​the electrode plate, in square centimeters (cm²) 2 );

[0018] C – Lithium-ion bulk concentration in battery materials, expressed in moles per cubic centimeter (mol / cm³) 3 );

[0019] σ – Warburg coefficient.

[0020] Preferably, in step S3, the lithium-ion bulk concentration C in the lithium-ion battery material is calculated using the following formula:

[0021]

[0022] In the formula:

[0023] N – Number of lithium ions in a single crystal cell;

[0024] N A —Avogadro's constant, 6.02 × 10⁻⁶ 23 mol -1 ;

[0025] V – Unit cell volume, measured in cubic angstroms.

[0026] Preferably, in step S3, ≥10 impedance data points in the low-frequency region where the angular frequency ω approaches 0 from step S2 are selected to plot Z′ and ω. -1 / 2 The curves (full cell, positive / reference cell, negative / reference cell) yield the corresponding Warburg coefficient σ, and the formula for calculating σ is:

[0027] Z′=R s +R ct +σω -1 / 2 ;

[0028] In the formula:

[0029] Z′——Impedance of a lithium-ion three-electrode battery, in ohms (Ω);

[0030] R s — Ohmic impedance of a lithium-ion three-electrode battery, in ohms (Ω);

[0031] R ct — Charge transfer impedance of a lithium-ion three-electrode battery, in ohms (Ω);

[0032] σ—Warburg coefficient;

[0033] ω — angular frequency, measured in radians per second (rad / s).

[0034] Preferably, the lithium-ion three-electrode battery is one of a pouch-type three-electrode battery and a coin-type three-electrode battery. When a pouch-type three-electrode battery is selected, before lithium plating in step S1, the pouch-type three-electrode battery is first prepared. The preparation method is as follows:

[0035] A single-piece soft-pack battery is manufactured through a process of slurry mixing, coating (single-layer coating is required for both positive and negative electrodes), rolling, and laser slicing. The size of a single soft-pack battery is 4×5cm. Copper wires, which have been ultrasonically cleaned (by sequentially using concentrated sulfuric acid, dilute sulfuric acid, and ultrapure water), are placed in the middle between the positive and negative electrodes of the soft-pack battery. Another separator is then attached in the same position as the original separator. Green adhesive is used to fix the copper wires between the two separators to obtain a soft-pack three-electrode battery. The diameter of the copper wires is 30μm to 100μm. The assembled soft-pack battery is then encapsulated in an aluminum-plastic film and injected with electrolyte for later use.

[0036] Preferably, before lithium plating, the lithium-ion three-electrode battery is charged / discharged for 2 weeks using a 0.05C current. The upper and lower limits of the charging voltage are set according to the different battery material types to activate the battery and stabilize the battery system.

[0037] Preferably, in step S1, a current of 20–40 μA is used to perform lithium plating on the reference electrode through the positive and negative electrodes.

[0038] Preferably, the length of the lithium-plated electrode is 10–15 cm, and the thickness of the lithium plating layer is 3–15 μm. Lithium plating refers to the process of reducing lithium metal ions in the positive / negative electrode of a lithium-ion battery to lithium metal atoms through an electrode reaction under the action of an external electric field, and then depositing the lithium metal on a reference electrode (copper wire) to form a lithium metal plating layer. Lithium plating includes forward and reverse lithium plating. Forward lithium plating involves connecting the test leads of a battery tester to the positive and reference electrodes of a three-electrode pouch battery and charging with a small current for 4–6 hours. Reverse lithium plating involves connecting the test leads of a battery tester to the negative and reference electrodes of a three-electrode pouch battery and charging with a small current for 4–6 hours.

[0039] Preferably, in step S1, after lithium plating of the lithium-ion three-electrode battery, the lithium-ion three-electrode battery is adjusted to different SOC (state of charge), charged with a constant current of 0.1 to 0.2C to the charging termination voltage specified by the enterprise, and left to stand for 1 hour. Then, it is discharged with a constant current of 0.1C to the discharge termination voltage specified by the enterprise, and left to stand for 1 hour. This cycle is repeated 3 to 5 times, and the capacity value of the last charge is taken as the actual capacity. Then, it is charged with a constant current of 0.1C (actual capacity) for 5 hours, and the SOC is adjusted to 50% (if other SOCs need to be tested, they should be adjusted according to the test requirements).

[0040] Preferably, in step S2, an eight-electrode in-situ impedance testing method is used to obtain impedance data between the full cell, the positive electrode / reference electrode, and the negative electrode / reference electrode at the same time during the impedance test, thus avoiding errors in contact impedance and characteristic frequency caused by multiple operations.

[0041] To achieve the second objective mentioned above, this invention provides an application of a method for testing the lithium-ion diffusion coefficient in lithium-ion batteries, and applies the tested lithium-ion diffusion coefficient to electrochemical simulations.

[0042] The advantages of this invention are:

[0043] (1) The test method of the present invention has simple test steps, short test time, simple and easy-to-understand calculation formula, and can simplify and facilitate the complex calculation process, and quickly obtain the lithium ion diffusion coefficient in lithium ion battery materials.

[0044] (2) This invention can greatly improve R&D efficiency by applying the tested lithium-ion diffusion coefficient to electrochemical simulation. This invention can quickly obtain the diffusion coefficient of lithium-ion full cells, and the testing method is simple and has a short testing cycle. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the three-electrode impedance test of a lithium-ion battery in Embodiment 1 of the present invention, where the horizontal axis Z′ is the real part of the impedance and the vertical axis Z″ is the imaginary part of the impedance.

[0046] Figure 2 This is a schematic diagram of the three-electrode impedance test of a lithium-ion battery in Embodiment 2 of the present invention, where the horizontal axis Z′ is the real part of the impedance and the vertical axis Z″ is the imaginary part of the impedance.

[0047] Figure 3 Z′ and ω in Embodiment 1 of the present invention -1 / 2 Schematic diagram of the curve.

[0048] Figure 4 Z′ and ω in Embodiment 2 of the present invention -1 / 2 Schematic diagram of the curve. Detailed Implementation

[0049] 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. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] Example 1

[0051] A method for testing the lithium-ion diffusion coefficient in a lithium-ion battery includes the following steps:

[0052] S1. Assemble the soft-pack three-electrode battery. According to the design process requirements, lithium iron phosphate / graphite materials are slurry-coated, coated, and rolled to form a single soft-pack battery with a size of 4×5cm. During the electrode preparation process, a single-layer coating process is required. Copper wire, after special treatment (sequential ultrasonic cleaning with concentrated sulfuric acid, dilute sulfuric acid, and ultrapure water), is placed in the middle between the positive and negative electrodes of the soft-pack battery. A separator is then attached, positioned in the same place as the original separator, and green adhesive is used to fix the copper wire between the two separators. The assembled soft-pack battery is then encapsulated in an aluminum-plastic film and filled with electrolyte for later use.

[0053] S2. Perform a 2-cycle charge-discharge cycle on a lithium iron phosphate / graphite monolithic soft-pack three-electrode battery at a current of 0.05C. The upper and lower limits of the charging voltage are set according to the different battery material types, wherein the voltage range of lithium iron phosphate / graphite material is 2.5~3.65V.

[0054] S3. Lithium plating is performed on the reference electrode using a 20μA current. Lithium plating refers to the process of reducing lithium metal ions in the positive / negative electrodes of a lithium-ion battery to lithium metal atoms through an electrode reaction under the influence of an external electric field, and then depositing the lithium metal onto the reference electrode (copper wire) to form a lithium metal coating. Lithium plating includes both forward and reverse plating. Forward plating involves connecting the test leads of the battery tester to the positive and reference electrodes of the three-electrode pouch battery and charging with a small current for 4 hours. Reverse plating involves connecting the test leads of the battery tester to the negative and reference electrodes of the three-electrode pouch battery and charging with a small current for 4 hours. The length of the lithium plating electrode is approximately 10cm, and the thickness of the lithium plating layer is 8μm.

[0055] S4. Adjust the SOC of the single soft-pack battery at different times, charge it at a constant current of 0.1C to the charging termination voltage specified by the company, let it rest for 1 hour, discharge it at a constant current of 0.1C to the discharging termination voltage specified by the company, let it rest for 1 hour, repeat this cycle 3 times, and take the capacity value of the last charge as the actual capacity. Charge it at a constant current of 0.1C (actual capacity) for 5 hours, and adjust the SOC to 50%.

[0056] S5. The impedance data of the full cell, positive electrode-reference electrode, and negative electrode-reference cell in a three-electrode pouch cell were measured using the in-situ electrochemical impedance spectroscopy method. The voltage perturbation value was set to 5mV, and the frequency range was 10. 5 Hz~0.01Hz; test data as follows Figure 1 As shown;

[0057] S6. Experimental data processing: Select at least 10 data points in the low-frequency region where angular frequency ω→0, and plot Z′ against ω. -1 / 2 Curves (full cell, positive-reference cell, negative-reference cell), where ω=2Πf, yield the corresponding Warburg coefficient σ. Figure 3 The slope of the curve is the Warburg coefficient σ. Then, based on Fick's second law and the Nernst equation, the formula for the lithium-ion diffusion coefficient is obtained. Substituting the corresponding parameters into the formula, the lithium-ion diffusion coefficient is calculated, as shown in Table 1 below. The lithium-ion diffusion coefficient formula is as follows:

[0058]

[0059] Table 1. Diffusion coefficient values ​​of the three-electrode pouch cell full cell (positive and negative parameters).

[0060] type σ <![CDATA[DLi+(cm 2 / s)]]> All battery 0.00389 3.49677E-11 Positive electrode (LFP) - Reference electrode 0.00262 7.70839E-11 Negative electrode (graphite) - Reference electrode 0.00133 2.99132E-10

[0061] Example 2

[0062] A method for testing the lithium-ion diffusion coefficient in a lithium-ion battery includes the following steps:

[0063] This invention provides a three-electrode electrochemical impedance spectroscopy method for measuring the lithium-ion diffusion coefficient in lithium-ion battery materials. The method includes the following steps:

[0064] S1. Assemble the soft-pack three-electrode battery. According to the design process requirements, ternary / graphite materials are processed through slurry mixing, coating, rolling, laser slicing, winding / stacking to form a single soft-pack battery. The size of a single soft-pack battery is 4×5cm. During the electrode preparation process, a single-layer coating process is required. Copper wire, after special treatment (sequential ultrasonic cleaning with concentrated sulfuric acid, dilute sulfuric acid, and ultrapure water), is placed in the center between the positive and negative electrodes of the soft-pack battery. A separator is then attached, in the same position as the original separator, and green adhesive is used to fix the copper wire between the two separators. The assembled soft-pack battery is then encapsulated in an aluminum-plastic film and injected with electrolyte for later use.

[0065] S2. Perform a 2-cycle charge-discharge cycle on a ternary / graphite monolithic soft-pack three-electrode battery at a current of 0.05C. The upper and lower limits of the charging voltage are set according to the different battery material types. Typically, the voltage range for ternary / graphite materials is 3.0 to 4.25V.

[0066] S3. Lithium plating is performed on the reference electrode using a 20μA current. Lithium plating refers to the process of reducing lithium metal ions in the positive / negative electrodes of a lithium-ion battery to lithium metal atoms through an electrode reaction under the influence of an external electric field, and then depositing the lithium metal onto the reference electrode (copper wire) to form a lithium metal coating. Lithium plating includes both forward and reverse plating. Forward plating involves connecting the test leads of the battery tester to the positive and reference electrodes of the three-electrode pouch battery and charging with a small current for 4 hours. Reverse plating involves connecting the test leads of the battery tester to the negative and reference electrodes of the three-electrode pouch battery and charging with a small current for 4 hours. The length of the lithium plating electrode is approximately 10cm, and the thickness of the lithium plating layer is 8μm.

[0067] S4. Assemble the three electrodes using a coin cell, adjust the coin cell to different SOC states, charge at a constant current of 0.1C to the charging termination voltage specified by the company, let it rest for 1 hour, discharge at a constant current of 0.1C to the discharging termination voltage specified by the company, let it rest for 1 hour, repeat this cycle 5 times, and take the capacity value of the last charge as the actual capacity. Charge at a constant current of 0.1C (actual capacity) for 5 hours, and adjust the SOC to 50%;

[0068] S5. The impedance data of the full cell, positive electrode-reference electrode, and negative electrode-reference cell in a three-electrode pouch cell were measured using the in-situ electrochemical impedance spectroscopy method. The voltage perturbation value was set to 5mV, and the frequency range was 10. 5 Hz~0.01Hz, test data as follows Figure 2 As shown;

[0069] S6. Experimental data processing: Select at least 10 data points in the low-frequency region where angular frequency ω→0, and plot Z′ against ω. -1 / 2 Curves (full cell, positive-reference cell, negative-reference cell), where ω=2Πf, yield the corresponding Warburg coefficient σ. Figure 4 The slope of the curve is the Warburg coefficient σ. Based on Fick's second law and the Nernst equation, the formula for the lithium-ion diffusion coefficient is obtained. Substituting the corresponding parameters into the formula, the lithium-ion diffusion coefficient is calculated, as shown in Table 2 below. The formula for the lithium-ion diffusion coefficient is as follows:

[0070]

[0071] Table 2. Diffusion coefficient values ​​for the full cell, positive-parameter, and negative-parameter three-electrode pouch cell.

[0072] type σ <![CDATA[DLi+(cm 2 / s)]]> All battery 0.084 2.39792E-16 Positive electrode (NCM) - Reference electrode 0.0372 4.70287E-17 Negative electrode (graphite) - Reference electrode 0.0398 5.38323E-17

[0073] Example 3

[0074] A method for testing the lithium-ion diffusion coefficient in a lithium-ion battery includes the following steps:

[0075] S1. Assemble the button cell three-electrode battery. According to the design process requirements, lithium iron phosphate / graphite material is slurryed, coated, rolled, and then cut into 12mm diameter discs using a round die to form the button cell three-electrode battery. A specially treated copper wire (concentrated sulfuric acid-dilute sulfuric acid-ultrapure water ultrasonic cleaning in sequence) is placed in the middle of the positive and negative electrode plates of the button cell three-electrode battery. Then, a separator is attached in the same position as the original separator. Green glue is used to fix the copper wire between the two separators. The assembled button cell battery is ready for use.

[0076] S2. Perform a 2-cycle charge-discharge cycle on a lithium iron phosphate / graphite button cell with a current of 0.05C. The upper and lower limits of the charging voltage are set according to the different battery material types. The voltage range for lithium iron phosphate / graphite materials is 2.5 to 3.65V.

[0077] S3. Lithium plating is performed on the reference electrode using a 20μA current. Lithium plating refers to the process of reducing lithium metal ions in the positive / negative electrodes of a lithium-ion battery to lithium metal atoms through an electrode reaction under the action of an external electric field, and then depositing the lithium metal onto the reference electrode (copper wire) to form a lithium metal coating. Lithium plating includes both forward and reverse plating. Forward plating involves connecting the test leads of the battery tester to the positive and reference electrodes of the coin cell three-electrode battery with a small current and charging for 4 hours. Reverse plating involves connecting the test leads of the battery tester to the negative and reference electrodes of the coin cell three-electrode battery with a small current and charging for 4 hours. The length of the lithium plating electrode is approximately 10cm, and the thickness of the lithium coating is 8μm.

[0078] S4. Adjust the button cell to different SOC states, charge at a constant current of 0.1C to the charging termination voltage specified by the company, let it rest for 1 hour, discharge at a constant current of 0.1C to the discharging termination voltage specified by the company, let it rest for 1 hour, repeat this cycle 3 times, and take the capacity value of the last charge as the actual capacity. Charge at a constant current of 0.1C (actual capacity) for 5 hours, and adjust the SOC to 50%;

[0079] S5. The impedance data of the full cell, positive electrode-reference electrode, and negative electrode-reference cell in a coin cell three-electrode battery are measured using the in-situ electrochemical impedance spectroscopy method. The voltage perturbation value is set to 5mV, and the frequency range is 10. 5 Hz~0.01Hz;

[0080] S6. Experimental data processing: Select at least 10 data points in the low-frequency region where angular frequency ω→0, and plot Z′ against ω. -1 / 2 Curves (full cell, positive-reference cell, negative-reference cell) are plotted, where ω = 2πf, yielding the corresponding Warburg coefficient σ. Then, based on Fick's second law and Nernst's equation, the formula for the lithium-ion diffusion coefficient is obtained. Substituting the corresponding parameters into the formula, the lithium-ion diffusion coefficient is calculated.

[0081] Table 3 Comparison of Lithium Ion Bulk Concentration in Lithium-ion Battery Materials

[0082]

[0083] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing the lithium-ion diffusion coefficient in a lithium-ion battery, characterized in that, The specific steps are as follows: S1. Assemble a lithium-ion three-electrode battery and use current to plate lithium on the reference electrode of the lithium-ion three-electrode battery to obtain a lithium-plated lithium-ion three-electrode battery. S2. The impedance data of the full cell, positive electrode / reference electrode, and negative electrode / reference cell in the lithium-ion three-electrode battery after lithium plating are measured using the in-situ electrochemical impedance spectroscopy method. The voltage perturbation value is set to 5-10mV, and the frequency is 0.01Hz-10Hz. 5 Hz; S3. Process the impedance data to obtain the corresponding Warburg coefficient σ, and calculate the lithium-ion diffusion coefficient using the following formula: In the formula: D Li+ —The diffusion coefficient of lithium ions in battery materials, expressed in square centimeters per second; R—ideal gas constant, 8.314 J / (mol·K); T – Test temperature, in Kelvin; n—the number of electrons transferred in a chemical reaction; F—Faraday constant, 96500 C / mol; A – Area of ​​the electrode plate, in square centimeters; C – Lithium ion bulk concentration in battery materials, in moles per cubic centimeter; σ – Warburg coefficient.

2. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that, In step S3, the lithium-ion bulk concentration C in the lithium-ion battery material is calculated using the following formula: In the formula: N – Number of lithium ions in a single crystal cell; N A —Avogadro's constant, 6.02 × 10⁻⁶ 23 mol -1 ; V – Unit cell volume, measured in cubic angstroms.

3. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that, In step S3, select ≥10 impedance data points in the low-frequency region from step S2 to plot Z′ and ω. -1 / 2 The curves yield the corresponding Warburg coefficients σ, and the formula for calculating σ is: Z′=R s +R ct +σω -1 / 2 ; In the formula: Z′——Lithium-ion three-electrode battery impedance, in ohms; R s — Ohmic impedance of a lithium-ion three-electrode battery, in ohms; R ct — Charge transfer impedance of a lithium-ion three-electrode battery, in ohms; σ—Warburg coefficient; ω – angular frequency, measured in radians per second.

4. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that: The lithium-ion three-electrode battery is one of a pouch three-electrode battery and a button three-electrode battery.

5. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that: Before lithium plating, the lithium-ion three-electrode battery is charged / discharged for 2 weeks using a 0.05C current.

6. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that: In step S1, a current of 20–40 μA is used to pass through the positive and negative electrodes to perform lithium plating on the reference electrode.

7. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that: In step S1, the length of the lithium-plated electrode is 10-15 cm, and the thickness of the lithium plating layer is 3-15 μm.

8. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that: In step S1, after lithium plating of the lithium-ion three-electrode battery, the different SOC states of the lithium-ion three-electrode battery are adjusted. The battery is charged with a constant current of 0.1 to 0.2C to the charging termination voltage specified by the enterprise, and then left to stand for 1 hour. The battery is then discharged with a constant current of 0.1C to the discharge termination voltage specified by the enterprise, and left to stand for 1 hour. This cycle is repeated 3 times, and the capacity value of the last charge is taken as the actual capacity. The battery is then charged with a constant current of 0.1C for 5 hours, and the SOC is adjusted to 50%.

9. The method for testing the lithium-ion diffusion coefficient in a lithium-ion battery according to claim 1, characterized in that: In step S2, an eight-electrode in-situ impedance testing method is used to obtain impedance data between the full cell, the positive electrode / reference electrode, and the negative electrode / reference electrode at the same time during the impedance test.

10. The application of the method for testing the lithium-ion diffusion coefficient in a lithium-ion battery as described in any one of claims 1-9, characterized in that: The lithium-ion diffusion coefficient obtained from the test was applied to electrochemical simulation.

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