Method for measuring electrolyte transference number of full-sea-depth pressure-bearing lithium ion battery
By forming and compacting a metallic lithium layer on the surface of a conductive metal using a lithium-plated blocking electrode and combining it with electrochemical workstation measurements, the difficulty in measuring the electrolyte migration number of lithium-ion batteries in deep-sea environments was solved, ensuring the performance evaluation and design of lithium-ion batteries in deep-sea pressure environments.
Patent Information
- Application Number
- CN202510924374.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-04
- Publication Date
- 2025-10-17
AI Technical Summary
In the existing technology, conventional methods cannot accurately measure the lithium ion migration number of lithium-ion battery electrolytes in deep-sea environments, making it difficult to evaluate the performance of lithium-ion batteries in deep-sea pressure environments.
A lithium-plated blocking electrode was used to form a metallic lithium layer on the surface of the conductive metal through the electrochemical lithium plating method, and then compaction treatment was performed. The electrolyte migration number was measured in combination with an electrochemical workstation, and the measurement was carried out in a simulated deep-sea pressure environment.
It effectively avoids the damage of deep-sea pressure to blocked electrodes, provides reliable lithium-ion transference number measurement results, supports the design of deep-sea lithium-ion batteries and electrolyte selection and modification, and improves the operational safety of batteries.
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Figure CN120801447A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of batteries, in particular to a method for measuring the electrolyte transference number of full-ocean-depth pressure-bearing lithium ion battery. BACKGROUND
[0002] Lithium ion batteries have become the most potential deep-sea equipment batteries due to their high specific energy and high specific power characteristics. Currently, there are mainly two ways when lithium ion batteries are used as power supply for deep-sea equipment: in relatively shallow waters, lithium ion battery packs rely on high-strength metal sealed shells to withstand seawater pressure or place the battery pack inside the pressure-bearing cabin of the deep-sea equipment, at this time the lithium ion battery monomers inside the battery pack do not bear the task of seawater pressure, and their design and examination requirements are similar to those of lithium ion battery monomers used in electric vehicles or energy storage power stations under normal pressure. However, as the depth continues to increase, in order to resist seawater pressure, the metal shell of the battery pack needs to be thicker and heavier, which is far more than the total weight of the battery monomers inside the battery, and also makes the overall shell design of the deep-sea equipment more complex, which greatly reduces the overall efficiency of the power supply. At this time, another design method is needed: the battery pack transmits the seawater pressure to all components immersed in the battery pack insulation oil through a light pressure supplementing film, so that all components including battery monomers have the ability to directly bear seawater pressure, so the metal shell can use the ordinary sealed shell under normal pressure. This design method allows the battery pack to be placed randomly outside the pressure-bearing cabin of the deep-sea equipment, with high mass specific energy and volume specific energy, and is becoming the mainstream technology route for deep-sea equipment batteries. Therefore, whether the high specific energy lithium ion battery monomer can withstand the huge seawater pressure of the deep sea has become the primary problem restricting the development of deep-sea equipment battery technology. As one of the three main raw materials of pressure-bearing deep-sea lithium ion battery monomers (positive electrode, negative electrode, and electrolyte), whether the lithium ion electrolyte can still maintain high-efficiency lithium ion transport capacity under deep-sea pressure will directly affect the performance of the battery monomer.
[0003] Lithium ion transference number refers to the proportion of lithium ion contribution to electrical conductivity. In the full-ocean-depth pressure environment, the high or low of lithium ion transference number is directly related to the discharge rate of the battery. Therefore, when designing pressure-bearing battery monomers, the lithium ion transference number in the electrolyte formula must be accurately characterized first. In the field of lithium ion battery electrolyte research, the measurement method under normal pressure is to use metallic lithium as a blocking electrode for lithium ions in the electrolyte, and to use a combination of AC impedance method and DC polarization method for measurement. However, the metallic lithium blocking electrode commonly used in this method will crack under deep-sea pressure, and even detach from the conductive network, losing the function of blocking other ions, which makes the conventional electrolyte transference number measurement method unsuitable for measuring the lithium ion transference number of deep-sea battery electrolyte. Therefore, it is urgent to develop a measurement method for the lithium ion transference number of electrolyte suitable for direct pressure-bearing battery research. SUMMARY
[0004] The present application aims to overcome the above technical deficiencies, and provide a full-ocean-depth pressure lithium-ion battery electrolyte migration number measurement method, which solves the technical problem that the lithium-ion migration number of the direct pressure battery electrolyte is difficult to measure in the prior art.
[0005] To achieve the above technical purpose, the technical scheme provided by the present application is: In a first aspect, the present application provides a full-ocean-depth pressure lithium-ion battery electrolyte migration number measurement method, comprising the following steps: S1, assembling an aluminum plastic film battery model with a lithium-plated blocking electrode, a battery separator and a to-be-measured electrolyte; the lithium-plated blocking electrode comprises a conductive metal and a metal lithium layer arranged on the surface of the conductive metal and subjected to compaction treatment; S2, pressurizing the aluminum plastic film battery model, and measuring the electrolyte migration number before and after pressurization and during pressurization; S3, judging the effectiveness of the electrolyte migration number during pressurization according to the electrolyte migration number before and after pressurization, and completing the full-ocean-depth pressure lithium-ion battery electrolyte migration number measurement.
[0006] In a second aspect, the present application provides an application of the above measurement method in electrolyte selection and modification in a full-ocean-depth lithium-ion battery.
[0007] Compared with the prior art, the present application has the following beneficial effects: The present application uses a metal lithium layer and prepares a lithium-plated blocking electrode by compaction treatment, which is used in the measurement of the electrolyte migration number of the pressure lithium-ion battery, can avoid the adverse factors caused by the damage of the deep-sea hydrostatic pressure to the lithium-ion blocking electrode, measure the migration number of lithium ions in the electrolyte under the deep-sea pressure environment, has good test reliability, and is convenient for analyzing the ion transport behavior of the electrolyte of the pressure lithium-ion battery under the deep-sea pressure environment, and provides technical support for improving the operation safety of the full-ocean-depth lithium-ion battery; at the same time, it can also be used as an important means for electrolyte selection and modification in the full-ocean-depth lithium-ion battery, and provides an important theoretical basis for the design of the direct pressure lithium battery in the deep-sea environment. BRIEF DESCRIPTION OF DRAWINGS
[0008] Figure 1 is a flowchart of the full-ocean-depth pressure lithium-ion battery electrolyte migration number measurement method of the present application; Figure 2 is the electrolyte migration number test data before pressurization in Example 2; wherein (a) is the initial AC impedance diagram, (b) is the current-time diagram, and (c) is the AC impedance diagram when the current is in a steady state; Figure 3 is the electrolyte migration number test data during pressure maintenance in Example 2; wherein (a) is the initial AC impedance diagram, (b) is the current-time diagram, and (c) is the AC impedance diagram when the current is in a steady state; Figure 4 is the test data of the electrolyte transference number after pressurization of Example 2; wherein (a) is the initial AC impedance diagram, (b) is the current-time diagram, and (c) is the AC impedance diagram when the current is in a steady state. DETAILED DESCRIPTION
[0009] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.
[0010] In the field of lithium ion battery electrolyte research, the measurement method under normal pressure is to use lithium metal as a blocking electrode for lithium ions in the electrolyte, and to measure by combining AC impedance method and direct current polarization method. However, the ordinary lithium ion blocking electrode has the following disadvantages in deep sea environment or in a pressure cylinder simulating deep sea environment test: on the one hand, the surface of the lithium metal is easily crushed during the conventional pressurization process, and microcracks occur, resulting in inaccurate transference number test, on the other hand, the lithium metal blocking electrode and the conductive metal are separated under high hydrostatic pressure, resulting in test failure.
[0011] The inventor found that although electrochemical lithium plating can avoid the pores between the lithium metal and the current collector, the surface of the blocking electrode not subjected to pressure cylinder pressurization generally has a loose structure and unstable SEI, and the test is unstable due to the irreversible changes of part of the electrode itself and the subsequent blocking electrode test at a too fast rate. Based on this, the present application is established.
[0012] The present application adopts the method of electrochemical lithium plating and approximate equilibrium pressurization to avoid the disadvantages in the prior art, and can simulate the full-ocean-depth pressurization process (including deep sea environment) to measure the transference number of lithium ion battery, which can avoid the adverse factors caused by the damage of deep sea hydrostatic pressure to the lithium ion blocking electrode, measure the transference number of lithium ion in the electrolyte under deep sea pressure environment, and provide an important theoretical basis for the design of direct pressure type lithium battery in deep sea environment.
[0013] In a first aspect, referring to Figure 1 The present application provides a full-ocean-depth pressurized lithium ion battery electrolyte transference number measurement method, comprising the following steps: S1, assembling an aluminum-plastic film battery model with a lithium plating blocking electrode, a battery separator and a to-be-tested electrolyte; the lithium plating blocking electrode comprises a conductive metal and a metal lithium layer arranged on the surface of the conductive metal and subjected to compaction treatment; S2, pressurizing the aluminum-plastic film battery model, and measuring the transference number of the electrolyte before and after pressurization and during pressurization; S3, according to the electrolyte migration number before and after pressurization, the effectiveness of the electrolyte migration number in the pressurization process is judged, and the electrolyte migration number measurement of the full-sea-depth pressure lithium ion battery is completed.
[0014] In the technical scheme of the present application, a lithium-plated blocking electrode for measuring the electrolyte migration number of a full-sea-depth pressure lithium ion battery is provided, which is provided with a metal lithium layer on the surface of a conductive metal and is subjected to compaction treatment, has the characteristics of reversible elasticity at 0-11000 meters, can keep the structure and chemical composition stable in the simulated deep-sea pressure environment, avoids cracking during testing, and makes the to-be-tested electrolyte not continuously react with the metal lithium layer.
[0015] Preferably, in step S1, the positive electrode and the negative electrode of the aluminum plastic film battery model are both the lithium-plated blocking electrode provided by the present application, and the battery separator is located between the positive electrode and the negative electrode. The battery separator is a polymer composite separator commonly used in the lithium ion industry, and the model is Celgard2325 with a thickness of 25 microns.
[0016] Preferably, in step S1, the to-be-tested electrolyte is prepared into 1M electrolyte with DMC for testing.
[0017] Preferably, in step S1, the conductive metal does not have a corrosion reaction with the to-be-tested electrolyte.
[0018] Preferably, in step S1, the conductive metal includes a metal foil with a thickness of 10-20 microns.
[0019] In the technical scheme of the present application, a metal foil is used as a conductor, including but not limited to a copper foil.
[0020] Preferably, in step S1, the thickness of the metal lithium layer is 15-25 microns.
[0021] Preferably, in step S1, the compaction treatment is performed by using a pressure cylinder, and the specific steps include: placing the conductive metal provided with the metal lithium layer into the pressure cylinder, uniformly increasing the pressure from normal pressure to above 114 MPa at a pressure increasing speed of not higher than 0.8 MPa / min, and releasing the pressure to normal pressure after pressure maintaining treatment.
[0022] In the technical scheme of the present application, the compaction treatment of the metal lithium layer is actually an approximate equilibrium pressure compaction by using a pressure cylinder, which can effectively compact the metal lithium layer while ensuring the stability of the electrode.
[0023] Further preferably, the pressure maintaining treatment is performed for 20-40 minutes, and the pressure is released to normal pressure at a speed of 4-6 MPa / min.
[0024] Preferably, after the compaction treatment, a cleaning step is further performed, in which the obtained compacted sample is cleaned with an inert organic solvent and then dried in vacuum.
[0025] Further preferably, the inert organic solvent includes dimethyl carbonate.
[0026] Preferably, in step S2, the electrolyte transference number is determined by an electrochemical workstation, using a combination of steady-state current and alternating current impedance.
[0027] Preferably, in step S2, the pressurizing process includes: pressurizing to a rated pressure P1 (MPa) at a pressurizing rate V1 (MPa / min) and holding for t1 (h); and depressurizing to normal pressure at a depressurizing rate ≥ 2 MPa / min, wherein V1 is within the adjustable parameter range of the pressurizing equipment; the pressure corresponding to the maximum seawater depth actually used by the lithium ion battery is P2, P1 ≥ P2; the time required for current balance (to reach a steady-state current) during actual measurement is t2, t1 > t2.
[0028] In the technical solution of the present application, V1 and P1 can be adjusted according to equipment parameters and actual testing needs; the holding time is determined according to the time of current balance during actual measurement. It can be understood that current balance is a parameter that can be routinely judged by those skilled in the art, i.e., a parameter in which the current no longer decreases significantly or changes little. The specific time taken to reach current balance or a period of time after reaching current balance has no effect on the test results, as long as t1 > t2.
[0029] Preferably, the effectiveness of the electrolyte transference number test during pressurization is determined according to the electrolyte transference number before and after pressurization, specifically including: the absolute value of the difference between the electrolyte transference number before and after pressurization is between 0 and 0.01, then the electrolyte transference number has repeatability, and the electrolyte transference number test during pressurization is effective; otherwise, the electrolyte transference number test during pressurization is ineffective.
[0030] Further preferably, the ion transference number is calculated by the following formula (1): (1) In formula (1), ΔV is a constant voltage (10 mV) applied to the aluminum-plastic film battery model, I0 is the initial current of each test, I S is the steady-state current of each test, R0 and R S are the interface resistances of the electrode and electrolyte at the beginning and at the steady state of each test, respectively; The effectiveness of the electrolyte transference number test during pressurization also includes: both before and after pressurization, R0 > R S , then the electrolyte transference number test during pressurization is effective, otherwise it is ineffective.
[0031] In a second aspect, the present application provides an application of the above-mentioned measurement method in electrolyte selection and modification in full-sea-depth lithium ion batteries.
[0032] Preferably, when the electrolyte migration number test during pressurization is effective, the electrolyte to be tested has a pressure resistance of 11000m.
[0033] The main working process and mechanism of the application include: (1) Preparation of full-ocean-depth pressure-resistant lithium ion blocking electrode: The conventional method for measuring lithium ion battery migration number is steady-state current method, which requires the use of a specially designed lithium-plated blocking electrode of the application. The electrode is plated with a layer of metallic lithium on the surface of a highly conductive metal that does not react with the electrolyte to be tested by electrochemical lithium plating. The metallic lithium is subjected to pressure resistance test in the following approximate equilibrium state: after being subjected to 0-11000m simulation pressure cylinder, the pressure cylinder test pressure holding time and pressure relief time are not required, but the first time the pressure is increased to meet: uniform speed from normal pressure to 127MPa, the pressure increasing speed should not be higher than 0.8MPa / min. The lithium-plated blocking electrode after pressure cylinder compaction is cleaned with inert organic solvent and vacuum dried.
[0034] (2) The electrolyte to be tested is loaded into an aluminum-plastic film battery model containing the above lithium-plated blocking electrode, and the electrolyte migration number before and after pressurization and during pressurization is tested by an electrochemical workstation. The steady-state current and alternating current impedance are combined to determine the ion migration number of the electrolyte. The ion migration number can be calculated by the above formula (1).
[0035] The measured lithium ion migration number t + The following conditions must be met simultaneously to consider the test results valid: ① The migration number test is done at least 3 times, including normal pressure test, in-situ test under simulated deep sea pressure, and migration number test after returning to normal pressure after pressure test; ② Before and after pressure test, R S , specifically, R 0前 before pressurization S前 and R 0后 after pressurization S后 (not comparing R0 before pressurization and R S after pressurization, or R0 after pressurization and R S before pressurization); before and after pressurization, R0>R S , the principle is that when and only when R0>R S , the sample to be tested does not react with the SEI formed on the surface of the blocking electrode under the pressure of the corresponding depth; ③ t +The electrolyte migration number difference before and after the pressure test has an absolute value of 0-0.01, which is repeatable; when the difference is too large, it indicates that the SEI formed on the surface of the blocked electrode under the pressure at the corresponding depth reacts; thus, the lithium plating blocked electrode of the present application is combined with the pressure-resistant lithium plating blocked electrode to determine whether the lithium ion migration number model is effective under the deep-sea pressure environment.
[0036] (3) The lithium plating blocked electrode of the present application has full-sea-depth pressure resistance: through experiments, it is found that the pressure increasing speed is 0.8 MPa / min at most, and the pressure maintaining pressure is 127 MPa at least, which is the boundary condition for compaction of the metal lithium layer obtained by electrochemical deposition into a stable structure of 0-11000 m. When the pressure increasing speed is higher than 0.8 MPa / min, the electrode is easily damaged; when the pressure increasing speed is lower than 0.8 MPa / min, the pressure maintaining pressure is 127 MPa, and the production time is longer, which is not economical (the pressure cylinder test is about 100,000 yuan / day).
[0037] Therefore, the present application is a method for detecting the lithium ion transmission performance of an electrolyte under full-sea-depth pressure, which is an important means for electrolyte selection and modification in a full-sea-depth lithium ion battery; at the same time, the present application can also analyze the ion transport behavior of the electrolyte of the full-sea-depth pressure-resistant lithium ion battery under the deep-sea pressure environment, study the influence of high hydrostatic pressure on the interaction between lithium salt and solvent in the electrolyte, and provide technical support for improving the operation safety of the full-sea-depth lithium ion battery.
[0038] The present application will be further described in detail through specific examples. In order to avoid redundancy, the main instruments and test conditions are described as follows: electrochemical workstation Z-pro; atmospheric pressure: local atmospheric pressure (86-106 kPa); indoor, ambient temperature 25℃±2℃, humidity 25%-65%.
[0039] Example 1 (lithium plating blocked electrode) A 25 μm metal lithium layer is plated on the surface of a 14 μm metal copper foil to obtain sample A; sample A is placed in a pressure cylinder, the pressure cylinder is uniformly increased from atmospheric pressure to 127 MPa at a pressure increasing speed of 0.8 MPa / min, and then maintained for 30 min, and then released to atmospheric pressure at a pressure releasing speed of 5 MPa / min to obtain sample B compacted by the pressure cylinder; sample B is cleaned with DMC solvent with a purity of 99.95%, and then dried in vacuum to obtain a lithium plating blocked electrode, which is placed in an inert gas glove box for use.
[0040] Example 2 (lithium plating blocked electrode) A full-sea-depth pressure-resistant lithium ion battery electrolyte migration number measurement method, comprising the following steps: S1, the lithium plating blocked electrode prepared in Example 1 and the electrolyte to be tested (1M LiPF6 DMC, water content ≤150 ppm) are assembled into a 1M LiPF6 DMC aluminum plastic film battery model; S2, pressurize the aluminum-plastic film battery model, and test the electrolyte transference number before and after pressurization and during the pressurization process; specifically comprising: S21, first use an electrochemical workstation to determine the transference number under normal pressure (AC impedance combined with DC polarization method, a commonly used method in the industry), conditions including: constant voltage 10 mV; obtain the electrolyte transference number before pressurization; S22, place the three aluminum-plastic film battery models (visually inspect the pressure-resistant aluminum-plastic film airbag appearance, which needs to be sealed and not leak) after measuring the transference number under normal pressure into a simulated pressure device (pressure working range: 0-144 MPa), place the pressurizing tool into the simulated pressure device, and connect the aluminum-plastic film battery model to the electrochemical workstation, start the pressurization system after checking the pressurization device, pressurize at a rate of 2 MPa / min to 115 MPa, maintain pressure for 2 hours, and then depressurize to normal pressure at a depressurization rate of ≥3 MPa / min, as shown in Table 1 below: Table 1 Pressurization and depressurization program
[0041] After the pressure cylinder pressure reaches 115 MPa, start measuring the transference number under pressure according to the method of transference number calibration under normal pressure, and obtain the electrolyte transference number during the pressurization process; During the measurement of the transference number, the pressure in the pressure cylinder environment should be maintained at 115 MPa, otherwise the measurement should be repeated; two samples of the same type should be tested under pressure on the same day to reduce the error caused by temperature; S23, transference number measurement after returning to normal pressure: when the pressure in the pressure cylinder is reduced to 0 (i.e., returning to normal pressure), after 30 minutes of static state, re-measure according to the method of transference number calibration under normal pressure, and obtain the electrolyte transference number after pressurization; S3, determine the validity of the electrolyte transference number test during the pressurization process according to the electrolyte transference number before and after pressurization, and complete the measurement of the electrolyte transference number of the full-ocean-depth pressure-bearing lithium ion battery.
[0042] The test data of the electrolyte transference number of this example (1M LiPF6 DMC) before and after pressurization and during the pressure maintaining process are shown in Table 2. Figures 2-4 The results are statistically analyzed and the electrolyte transference number is calculated, as shown in Table 2.
[0043] Table 2 Test data and results of the electrolyte transference number of Example 2
[0044] As shown in Table 2, before the pressurization test, the migration number of Example 1 was about 0.519, during the 115MPa pressure holding process, it was about 0.447, and in the normal pressure test after the pressurization, the migration number was about 0.521. s is 4.90 ohms, after pressurization R0 is 4.91 ohms, R s The ohm value is 3.98 ohms, which meets the criteria for valid electrolyte migration number testing during pressurization. This indicates that the 1M LiPF6DMC electrolyte has good pressure resistance and that pressure has little effect on the electrolyte. 1M LiPF6DMC has a pressure resistance of 11000 mΩ.
[0045] Comparative Example 1 The only difference from Example 2 is that 1M LiFSI DMC is used to replace the electrolyte in Example 2, and the other steps and conditions are the same as those in Example 2.
[0046] The electrolyte migration number test data of this comparative example (1M LiFSI DMC) before and after pressurization and during the pressure holding process were statistically analyzed and calculated to obtain the electrolyte migration number. The results are shown in Table 3.
[0047] Table 3 Electrolyte migration test data and results of Comparative Example 1
[0048] As shown in Table 3, before the pressurization test, the migration number of Comparative Example 1 was about 0.669, and during the 115MPa pressure holding process, it was about 0.472. After the pressurization, in the normal pressure test, the migration number was about 0.508. s is 1.40 ohms, after pressurization R0 is 1.16 ohms, R s It is 1.20 ohms, indicating that the migration number of the 1M LiFSI DMC electrolyte reacted with the blocked electrode in the pressure cylinder test under the simulated deep-sea environment, and its true value could not be measured, indicating that the 1M LiFSIDMC does not have the pressure resistance adaptability of 11000m.
[0049] Therefore, the lithium plating blocking electrode prepared by the method of electrochemical lithium plating and approximate balance voltage boosting is used in the measurement of the electrolyte migration number of the pressure-bearing lithium ion battery, the adverse factors caused by the damage of the deep-sea hydrostatic pressure to the lithium ion blocking electrode can be avoided, the migration number of lithium ions in the electrolyte under the deep-sea pressure environment can be measured, the ion transport behavior of the electrolyte of the full-ocean-depth pressure-bearing lithium ion battery under the deep-sea pressure environment can be analyzed, the influence of the high hydrostatic pressure on the interaction between the lithium salt and the solvent in the electrolyte can be studied, technical support for improving the operation safety of the full-ocean-depth lithium ion battery is provided, meanwhile, the method can also be used as an important means for the selection and modification of the electrolyte in the full-ocean-depth lithium ion battery, and important theoretical basis is provided for the design of the direct pressure-bearing lithium battery in the deep-sea environment. Meanwhile, the application sets multiple conditions to verify its effectiveness, and has good reliability.
[0050] The specific embodiments of the application described above do not constitute a limitation on the protection scope of the application. Any various other corresponding changes and modifications made according to the technical concept of the application shall be included in the protection scope of the claims of the application.
Claims
1. A method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery, characterized in that: The following steps are involved: S1, assembling an aluminum-plastic film battery model with a lithium-plated blocking electrode, a battery separator, and an electrolyte to be tested; the lithium-plated blocking electrode comprises a conductive metal and a metallic lithium layer disposed on the surface of the conductive metal and subjected to a compaction treatment; S2, pressurizing the aluminum-plastic film battery model and measuring the electrolyte migration number before, during and after pressurization; S3, judging the validity of the electrolyte migration number during the pressurization process based on the electrolyte migration number before and after pressurization, and completing the full-sea-depth pressurized lithium-ion battery electrolyte migration number measurement.
2. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 1, characterized in that: In step S1, the positive electrode and the negative electrode of the aluminum-plastic film battery model are both the lithium-plated blocking electrodes; and / or, The electrolyte to be tested is prepared into an electrolyte solution for testing; and / or, The conductive metal comprises a metal foil having a layer thickness of 10 to 20 μm; and / or, The thickness of the metal lithium layer is 15 to 25 μm.
3. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 1, characterized in that: In step S1, the compaction treatment is performed using a pressure cylinder, and the specific steps include: placing a conductive metal provided with a metallic lithium layer into a pressure cylinder, uniformly increasing the pressure from normal pressure to above 114 MPa at a pressure increasing rate not higher than 0.8 MPa / min, and releasing the pressure to normal pressure after the pressure maintenance treatment.
4. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 3, characterized in that: The time of the pressure maintaining treatment is 20 to 40 minutes, and the pressure is released to normal pressure at a speed of 4 to 6 MPa / min.
5. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 1, characterized in that: In step S1, after the compaction treatment, a cleaning step is performed, wherein the compacted sample is cleaned with an organic solvent and then vacuum-dried.
6. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 1, characterized in that: In step S2, the electrolyte migration number is measured by an electrochemical workstation using a method combining steady-state current and AC impedance.
7. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 1, characterized in that: In step S2, the pressurization process includes: pressurizing to the rated pressure P1 at a pressurization rate of V1 and maintaining the pressure for a time of t1; then unloading the pressure to normal pressure at a pressure relief rate of ≥ 2 MPa / min; wherein V1 is within the adjustable parameter range of the pressurization equipment; the pressure corresponding to the maximum seawater depth actually used by the lithium-ion battery is P2, P1 ≥ P2; the time required for the current to reach a steady state during the actual measurement process is t2, t1>t 2。 8. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 1, characterized in that: In step S3, judging the validity of the electrolyte migration number during the pressurization process based on the electrolyte migration number before and after pressurization specifically includes: If the absolute value of the difference between the electrolyte migration number before and after pressurization is between 0 and 0.01, the electrolyte migration number is repeatable and the electrolyte migration number test during pressurization is valid; otherwise, the electrolyte migration number test during pressurization is invalid.
9. The method for measuring the electrolyte migration number of a full-sea-depth pressurized lithium-ion battery according to claim 8, characterized in that: The ion migration number is calculated by formula (1): （1） In formula (1), ΔV is the constant voltage applied to the aluminum-plastic film battery model, I0 is the initial current of each test, and I S is the steady-state current for each test, R0 and R S are the interfacial impedances between the electrode and the electrolyte at the initial and steady-state stages of each test; The validity of the electrolyte migration number in the pressurization process is also determined by: R0>R S , then the electrolyte migration number test during the pressurization process is valid, otherwise it is invalid.
10. Application of the measurement method according to claim 9 in the selection and modification of electrolytes in lithium-ion batteries at full ocean depth.