In-situ evaluation method for mechanical properties of lithium ion battery

Abstract

The invention discloses a lithium ion battery mechanical property in-situ evaluation method, which comprises the following steps: step 1, taking a plurality of first lithium ion batteries, and carrying out impedance test on the plurality of first lithium ion batteries to correspondingly obtain a plurality of first electrochemical capacitance values; step 2, carrying out different times of charge-discharge cycle tests on the plurality of first lithium ion batteries, and completely discharging after multiple times of cycle tests are completed to obtain a plurality of second lithium ion batteries with different cycle times according to a certain cycle time interval; step 3, carrying out impedance test on the plurality of second lithium ion batteries to correspondingly obtain a plurality of second electrochemical capacitance values; and step 4, calculating a plurality of first and second specific surface area values according to the plurality of first and second electrochemical capacitance values, and evaluating the mechanical property of the battery according to the evolution trend of the difference between the plurality of second and first specific surface area values. By adopting the method, the mechanical property of the battery is rapidly evaluated, reverse optimization of battery design is facilitated, and the product development period is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to an in-situ evaluation method for the mechanical properties of lithium ion batteries. Background Art

[0002] As a key component of energy utilization and transformation, lithium-ion batteries play a vital role in aerospace equipment and other fields, and their performance is directly related to the success or failure of the mission. With the continuous improvement of application requirements, higher requirements are placed on the specific energy of batteries. An effective way to improve the specific energy of batteries is to use high specific capacity electrode materials.

[0003] At present, the energy storage battery system with high nickel ternary materials (nickel content higher than 80%) as the positive electrode and silicon-based composite materials as the negative electrode has become the development direction of high specific energy battery technology due to its significant high specific energy characteristics. However, the inherent large chemical strain of high specific capacity electrode materials makes high specific energy batteries face prominent structural mechanical failure problems, affecting battery performance. Specifically, the positive electrode material undergoes H2-H3 phase transition under charging, and the lattice produces significant anisotropic contraction or expansion, causing stress accumulation inside the material, and ultimately leading to a large number of microcracks inside the material, exposing the internal surface of the material, providing channels for electrolyte penetration and degradation, thereby deteriorating battery performance. On the other hand, the negative electrode material will undergo significant volume expansion and contraction during the charging and discharging process, causing cracks to form until it is pulverized, destroying the contact between the electrode material and the current collector, and causing rapid decay of the battery capacity.

[0004] Existing evaluation methods are often unable to monitor the changes in the mechanical properties of batteries in real time under actual working conditions, resulting in the inability to accurately predict and control the degradation of battery performance. Therefore, it is urgent to conduct in-situ evaluation of the mechanical properties of high-energy-density batteries to guide the design of high-energy-density batteries and support the formulation of service performance control strategies for high-energy-density batteries. Summary of the invention

[0005] The purpose of the present invention is to provide an in-situ evaluation method for the mechanical properties of a lithium-ion battery, by synchronously detecting the electrochemical capacitance values ​​of the positive electrode and the negative electrode under different cycle numbers to obtain the specific surface area values ​​of the positive electrode and the negative electrode, and obtaining the specific surface area value and change value of the whole battery, and quickly evaluating the mechanical properties of the lithium-ion battery according to the evolution trend of the specific surface area change value of the whole battery.

[0006] In order to achieve the above object, the present invention provides a method for in-situ evaluation of mechanical properties of a lithium-ion battery, the method comprising:

[0007] Step 1, taking a plurality of first lithium-ion batteries, performing impedance tests on the plurality of first lithium-ion batteries, and correspondingly obtaining a plurality of first electrochemical capacitance values;

[0008] Step 2, performing charge and discharge cycle tests of different numbers on the plurality of first lithium ion batteries, and fully discharging the batteries after completing the plurality of cycle tests, to obtain a plurality of second lithium ion batteries with different cycle numbers at certain cycle number intervals;

[0009] Step 3, performing impedance testing on a plurality of the second lithium-ion batteries to obtain a plurality of corresponding second electrochemical capacitance values;

[0010] Step 4: Calculate a plurality of first specific surface area values ​​and a second specific surface area value based on the plurality of first electrochemical capacitance values ​​and the second electrochemical capacitance values, and evaluate the mechanical properties of the lithium-ion battery based on the evolution trend of the difference between the plurality of second specific surface area values ​​and the first specific surface area values.

[0011] Optionally, before step 1, the method further comprises: establishing a relationship between the electrochemical capacitance of the positive electrode and the specific surface area of ​​the positive electrode; and establishing a relationship between the electrochemical capacitance of the negative electrode and the specific surface area of ​​the negative electrode.

[0012] Optionally, the impedance test is to synchronously detect the imaginary values ​​of the positive electrode and the negative electrode at the characteristic impedance frequency, and calculate several positive electrode first electrochemical capacitance values, positive electrode second electrochemical capacitance values, negative electrode first electrochemical capacitance values, and negative electrode second electrochemical capacitance values.

[0013] Optionally, according to several positive electrode first electrochemical capacitance values, positive electrode second electrochemical capacitance values ​​and the relationship between the positive electrode electrochemical capacitance and the positive electrode specific surface area, several positive electrode first specific surface area values ​​and positive electrode second specific surface area values ​​are calculated; according to several negative electrode first electrochemical capacitance values, negative electrode second electrochemical capacitance values ​​and the relationship between the negative electrode electrochemical capacitance and the negative electrode specific surface area, several negative electrode first specific surface area values ​​and negative electrode second specific surface area values ​​are calculated.

[0014] Optionally, in step 4, the first specific surface area value is the sum of the first specific surface area value of the positive electrode and the first specific surface area value of the negative electrode; the second specific surface area value is the sum of the second specific surface area value of the positive electrode and the second specific surface area value of the negative electrode.

[0015] Optionally, in step 1, a reference electrode is provided inside each of the first lithium-ion batteries; the reference electrode is isolated from the positive electrode and the negative electrode of the first lithium-ion battery by a diaphragm, and the reference electrode is connected to an external circuit of the first lithium-ion battery through a tab.

[0016] Optionally, in step 1, the positive electrode of the first lithium-ion batteries is any one of lithium nickel cobalt manganese oxide and its derivatives, lithium nickel cobalt aluminum oxide and its derivatives.

[0017] Optionally, in step 1, the negative electrodes of the first lithium-ion batteries include at least one of silicon-based materials and their derivatives, and graphite materials and their derivatives.

[0018] Optionally, in step 2, the cycle number interval is 20 to 200 times.

[0019] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0020] 1) Construct a lithium-ion battery with a reference electrode, establish the relationship between electrochemical capacitance and specific surface area, obtain the specific surface area values ​​of the positive and negative electrodes by synchronously detecting the electrochemical capacitance values ​​of the positive and negative electrodes at different cycle times, and obtain the specific surface area value and change value of the whole battery. According to the evolution trend of the specific surface area change value of the whole battery, the mechanical properties of the lithium-ion battery can be quickly evaluated, which is helpful to formulate the service performance control strategy of high specific energy batteries.

[0021] 2) Furthermore, the relationship between the specific surface area evolution trend and the number of cycles is obtained. Using the specific surface area values ​​of the positive and negative electrodes obtained at the same time, the contribution of the positive and negative electrodes to the evolution of the mechanical properties of the whole battery during the battery cycle can be analyzed, which is conducive to reverse optimization of battery design and greatly shortening the product development cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a flow chart of the in-situ evaluation method of mechanical properties of lithium-ion batteries.

[0023] Figure 2 It is an evolution trend diagram of the specific surface area change value of the full battery, positive electrode and negative electrode under different cycle numbers of the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0026] As described in the background technology, the inherent large chemical strain of high-capacity electrode materials makes high-energy-density batteries face prominent structural mechanical failure problems, affecting battery performance. Existing evaluation methods are often unable to monitor the changes in the mechanical properties of batteries under actual working conditions in real time, resulting in the inability to accurately predict and control the decline of battery performance. It is urgent to conduct in-situ evaluation of the mechanical properties of high-energy-density batteries to guide the design of high-energy-density batteries and support the formulation of their service performance control strategies.

[0027] The evaluation method of the present invention first establishes the relationship between electrochemical capacitance and specific surface area, obtains the specific surface area values ​​of the positive electrode and the negative electrode by detecting the electrochemical capacitance values ​​of the positive electrode and the negative electrode under different cycle numbers, obtains the specific surface area value and change value of the whole battery, and quickly evaluates the mechanical properties of the lithium-ion battery according to the evolution trend of the specific surface area change value of the whole battery; at the same time, the relationship between the specific surface area evolution trend and the cycle number is obtained, and the specific surface area values ​​of the positive electrode and the negative electrode obtained at the same time can be used to analyze the contribution of the positive electrode and the negative electrode to the evolution of the mechanical properties of the whole battery during the battery cycle, which is conducive to reverse optimization of battery design and greatly shortening the product development cycle.

[0028] Based on the above, the present invention provides a method for in-situ evaluation of mechanical properties of lithium-ion batteries, the process of which is as follows: Figure 1 As shown, the method comprises:

[0029] Step 1: Take a plurality of first lithium-ion batteries, perform impedance testing on the plurality of first lithium-ion batteries, and obtain a plurality of corresponding first electrochemical capacitance values.

[0030] The imaginary values ​​of the positive electrode and the negative electrode of the first lithium-ion battery at the characteristic impedance frequency are detected simultaneously by impedance testing, and the first electrochemical capacitance value of the positive electrode and the first electrochemical capacitance value of the negative electrode of each first lithium-ion battery are calculated according to the formula C=1 / (-Im(Z)), where C is the electrochemical capacitance and Im(Z) is the imaginary value. In this embodiment, the characteristic impedance frequency is a preset fixed value, and the method for determining the characteristic impedance frequency is: the relationship between the imaginary value at the characteristic impedance frequency measured by the impedance testing method for the electrode in a fully lithium-intercalated or fully lithium-deintercalated state and the electrochemical capacitance satisfies: C=1 / (-Im(Z)).

[0031] Before step 1, it also includes: establishing the relationship between electrochemical capacitance and specific surface area, and the establishment method is: loading different pressures on the positive electrode and the negative electrode respectively, using the Kr-BET method to test the specific surface areas of the positive electrode and the negative electrode, and using the impedance test method to detect the electrochemical capacitance of the positive electrode and the negative electrode at the characteristic impedance frequency. The specific surface area is the independent variable, the electrochemical capacitance is the dependent variable, and the relationship curve is fitted to obtain the relationship between the electrochemical capacitance of the positive electrode and the specific surface area of ​​the positive electrode: C1=k1S1, and the relationship between the electrochemical capacitance of the negative electrode and the specific surface area of ​​the negative electrode is: C2=k2S2; wherein C1 and C2 are the electrochemical capacitances of the positive electrode and the negative electrode, k1 and k2 are fixed coefficients, and S1 and S2 are the specific surface areas of the positive electrode and the negative electrode.

[0032] Step 2: performing charge-discharge cycle tests of different times on the first lithium-ion batteries, and then fully discharging them after completing multiple cycle tests, to obtain a plurality of second lithium-ion batteries with different cycle times at certain cycle time intervals.

[0033] A reference electrode is provided inside the first lithium-ion batteries. The reference electrode is used to test the potential of the positive electrode and the negative electrode in situ, accurately measure the electrode potential of the positive electrode and the negative electrode relative to the reference electrode, and ensure the accuracy of the test. The material of the reference electrode can be copper wire, metallic lithium or lithium alloy. The reference electrode is isolated from the positive electrode and the negative electrode by a diaphragm to prevent direct contact with the positive and negative electrodes, thereby avoiding the occurrence of short circuits. The reference electrode is connected to the external circuit of the battery through a pole ear. The pole ear is usually made of metal, and its material can be nickel or aluminum, which is used to collect the current on the reference electrode and conduct it out of the battery. There is no special limitation on the reference electrode in the present invention, and those skilled in the art can know it through conventional experimental methods.

[0034] In some embodiments, the positive electrode of the first lithium-ion battery is any one of lithium nickel cobalt manganese oxide and its derivatives, lithium nickel cobalt aluminum oxide and its derivatives, and the negative electrode of the first lithium-ion battery includes at least one of silicon-based materials and their derivatives, graphite materials and their derivatives.

[0035] In some embodiments, the cycle number interval is 20 to 200 times, and the cycle number is 100 to 500 times. As an example, the cycle number interval is set to 100 times, and the cycle number can be set to 100 times, 200 times, 300 times, 400 times or 500 times. After the cycle is completed, each first lithium-ion battery is fully discharged to 0% SOC to obtain a number of second lithium-ion batteries with different cycle numbers. After full discharge, the positive electrode is in a fully lithium-embedded state, that is, the lithium ions are fully embedded in the positive electrode; the negative electrode is in a fully delithiated state, that is, the lithium ions are completely removed from the negative electrode.

[0036] Step 3: performing impedance testing on a plurality of said second lithium-ion batteries to obtain a plurality of corresponding second electrochemical capacitance values.

[0037] The impedance test is used to simultaneously detect the imaginary part values ​​of the positive electrode and the negative electrode of the second lithium ion battery at the characteristic impedance frequency. According to the formula C=1 / (-Im(Z)), where C is the electrochemical capacitance and Im(Z) is the imaginary part value, the second electrochemical capacitance value of the positive electrode and the second electrochemical capacitance value of the negative electrode of each second lithium ion battery are calculated.

[0038] In this embodiment, the impedance test of the positive electrode and the negative electrode is carried out simultaneously using the main test channel and the auxiliary test channel in the electrochemical workstation, that is, the impedance data of the positive electrode and the negative electrode are detected simultaneously under one signal disturbance, so as to avoid the interference of the interface state fluctuation on the test result under multiple signal disturbances, which makes the electrochemical capacitance detection of the positive electrode and the negative electrode inaccurate.

[0039] Step 4: Calculate a plurality of first specific surface area values ​​and a second specific surface area value based on the plurality of first electrochemical capacitance values ​​and the second electrochemical capacitance values, and evaluate the mechanical properties of the lithium-ion battery based on the evolution trend of the difference between the plurality of second specific surface area values ​​and the first specific surface area values.

[0040] The first specific surface area values ​​of the plurality of positive electrodes are calculated based on the first electrochemical capacitance values ​​of the plurality of positive electrodes and the relationship between the electrochemical capacitance of the positive electrodes and the specific surface area of ​​the positive electrodes; the second specific surface area values ​​of the plurality of positive electrodes are calculated based on the second electrochemical capacitance values ​​of the plurality of positive electrodes and the relationship between the electrochemical capacitance of the positive electrodes and the specific surface area of ​​the positive electrodes.

[0041] The first specific surface area values ​​of the plurality of negative electrodes are calculated according to the first electrochemical capacitance values ​​of the plurality of negative electrodes and the relationship between the electrochemical capacitance of the negative electrodes and the specific surface area of ​​the negative electrodes; the second specific surface area values ​​of the plurality of negative electrodes are calculated according to the second electrochemical capacitance values ​​of the plurality of negative electrodes and the relationship between the electrochemical capacitance of the negative electrodes and the specific surface area of ​​the negative electrodes.

[0042] The first specific surface area value is the sum of the first specific surface area value of the positive electrode and the first specific surface area value of the negative electrode, the second specific surface area value is the sum of the second specific surface area value of the positive electrode and the second specific surface area value of the negative electrode, the first specific surface area value is the specific surface area value of the first lithium ion battery, and the second specific surface area value is the specific surface area value of the second lithium ion battery. The difference between the specific surface area values ​​of the second lithium ion battery and the first lithium ion battery is taken, and the mechanical properties of the lithium ion battery can be evaluated according to the evolution trend of the difference under different cycle numbers.

[0043] The change in the specific surface area of ​​the electrode is positively correlated with the degree of particle breakage and pulverization caused by the internal stress of the electrode. The larger the change in the specific surface area, the greater the particle deformation, the stronger the internal stress of the electrode, indicating that the mechanical properties are worse. Therefore, the change in the specific surface area of ​​the whole battery can be used as an important measure of the mechanical properties of lithium-ion batteries. The larger the change in the specific surface area of ​​the whole battery, the worse the mechanical properties of the battery are evaluated, and the smaller the change in the specific surface area of ​​the whole battery, the better the mechanical properties of the battery are evaluated. In this embodiment, by analyzing the contribution of the positive and negative electrodes to the evolution of the mechanical properties of the whole battery during the cycle, it is beneficial to reversely optimize the battery design and greatly shorten the product development cycle.

[0044] Example

[0045] Using nickel cobalt manganese oxide material (nickel content greater than 80%) as the positive electrode and a mixture of graphite material and pre-lithiated silicon oxide material as the negative electrode, five soft-packaged first lithium-ion batteries with a reference electrode were assembled. The rated capacity was 5Ah. The reference electrode was a copper wire, which was isolated from the positive and negative electrodes by a diaphragm and connected to the external circuit of the battery through a tab.

[0046] The impedance of the positive and negative electrodes of the five first lithium-ion batteries is tested simultaneously to determine that the characteristic impedance frequency is 180mHz, the imaginary part values ​​of the positive and negative electrodes at 180mHz are detected, and the first electrochemical capacitance values ​​of the five positive electrodes and the first electrochemical capacitance values ​​of the five negative electrodes are calculated.

[0047] A cycle test was performed on the five first lithium-ion batteries: at room temperature, each first lithium-ion battery was charged to 4.3V at a constant current of 0.5C, switched to constant voltage charging to a cutoff current of 0.05C, and allowed to stand for 10 minutes; then the battery was discharged to 2.8V at a constant current of 0.5C, and allowed to stand for 10 minutes. This process was used to cycle the five first lithium-ion batteries for 100, 200, 300, 400 and 500 times, respectively, and then all were discharged to 0% SOC to obtain five second lithium-ion batteries with different numbers of cycles.

[0048] The impedance of the positive and negative electrodes of the five second lithium-ion batteries was tested simultaneously to determine that the characteristic impedance frequency was 180 MHz. The imaginary values ​​of the positive and negative electrodes at 180 MHz were detected to calculate the second electrochemical capacitance values ​​of the five positive electrodes and the second electrochemical capacitance values ​​of the five negative electrodes.

[0049] The first specific surface area values ​​of the five positive electrodes are calculated based on the first electrochemical capacitance values ​​of the five positive electrodes and the relationship between the electrochemical capacitance of the positive electrode and the specific surface area of ​​the positive electrode; the first specific surface area values ​​of the five negative electrodes are calculated based on the first electrochemical capacitance values ​​of the five negative electrodes and the relationship between the electrochemical capacitance of the negative electrode and the specific surface area of ​​the negative electrode.

[0050] The second specific surface area values ​​of the five positive electrodes are calculated based on the second electrochemical capacitance values ​​of the five positive electrodes and the relationship between the electrochemical capacitance of the positive electrode and the specific surface area of ​​the positive electrode; the second specific surface area values ​​of the five negative electrodes are calculated based on the second electrochemical capacitance values ​​of the five negative electrodes and the relationship between the electrochemical capacitance of the negative electrode and the specific surface area of ​​the negative electrode.

[0051] The first specific surface area values ​​of the five positive electrodes and the first specific surface area values ​​of the five negative electrodes are added together to obtain the specific surface area values ​​of the five first lithium-ion batteries. The second specific surface area values ​​of the five positive electrodes and the second specific surface area values ​​of the five negative electrodes are added together to obtain the specific surface area values ​​of the five second lithium-ion batteries. The difference between the specific surface area values ​​of the five second lithium-ion batteries and the first lithium-ion battery is the change in specific surface area under different numbers of cycles.

[0052] like Figure 2 As shown, the change in the specific surface area of ​​the whole battery gradually increases with the increase in the number of cycles, indicating that as the number of cycles increases, the degree of particle rupture inside the whole battery becomes increasingly serious, and the mechanical properties become worse. At the same time, the change in the specific surface area of ​​the positive electrode at different cycle times is calculated by the difference between the five second specific surface area values ​​of the positive electrode and the first specific surface area value of the positive electrode. The change in the specific surface area of ​​the negative electrode at different cycle times is calculated by the difference between the five second specific surface area values ​​of the negative electrode and the first specific surface area value of the negative electrode. By comparison, it is found that the change in the specific surface area of ​​the positive electrode is smaller than the change in the specific surface area of ​​the negative electrode, indicating that the negative electrode contributes more to the evolution of the mechanical properties of the whole battery.

[0053] In summary, the present invention obtains the specific surface area values ​​of the positive electrode and the negative electrode by synchronously detecting the electrochemical capacitance values ​​of the positive electrode and the negative electrode under different cycle numbers, obtains the specific surface area value and change value of the whole battery, and quickly evaluates the mechanical properties of the lithium-ion battery according to the evolution trend of the change value of the specific surface area of ​​the whole battery; at the same time, the relationship between the specific surface area evolution trend and the cycle number is obtained, and the specific surface area values ​​of the positive electrode and the negative electrode obtained at the same time can be used to analyze the contribution of the positive electrode and the negative electrode to the evolution of the mechanical properties of the whole battery during the battery cycle, which is conducive to reverse optimization of battery design and greatly shortening the product development cycle.

[0054] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for in-situ evaluation of mechanical properties of lithium-ion batteries, characterized in that: The method includes: Step 1, taking a plurality of first lithium-ion batteries, performing impedance tests on the plurality of first lithium-ion batteries, and correspondingly obtaining a plurality of first electrochemical capacitance values; Step 2, performing charge and discharge cycle tests of different numbers on the plurality of first lithium ion batteries, and fully discharging the batteries after completing the plurality of cycle tests, to obtain a plurality of second lithium ion batteries with different cycle numbers at certain cycle number intervals; Step 3, performing impedance testing on a plurality of the second lithium-ion batteries to obtain a plurality of corresponding second electrochemical capacitance values; Step 4: Calculate a plurality of first specific surface area values ​​and a second specific surface area value based on the plurality of first electrochemical capacitance values ​​and the second electrochemical capacitance values, and evaluate the mechanical properties of the lithium-ion battery based on the evolution trend of the difference between the plurality of second specific surface area values ​​and the first specific surface area values.

2. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 1, characterized in that: Before step 1, the method further comprises: establishing a relationship between the electrochemical capacitance of the positive electrode and the specific surface area of ​​the positive electrode; Establish the relationship between the negative electrode electrochemical capacitance and the negative electrode specific surface area.

3. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 2, characterized in that: The impedance test is to synchronously detect the imaginary values ​​of the positive electrode and the negative electrode at the characteristic impedance frequency, and calculate several positive electrode first electrochemical capacitance values, positive electrode second electrochemical capacitance values, negative electrode first electrochemical capacitance values, and negative electrode second electrochemical capacitance values.

4. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 3, characterized in that: According to a number of positive electrode first electrochemical capacitance values, positive electrode second electrochemical capacitance values, and a relationship between the positive electrode electrochemical capacitance and the positive electrode specific surface area, a number of positive electrode first specific surface area values ​​and positive electrode second specific surface area values ​​are calculated; according to a number of negative electrode first electrochemical capacitance values, negative electrode second electrochemical capacitance values, and a relationship between the negative electrode electrochemical capacitance and the negative electrode specific surface area, a number of negative electrode first specific surface area values ​​and negative electrode second specific surface area values ​​are calculated.

5. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 4, characterized in that: In step 4, the first specific surface area value is the sum of the first specific surface area value of the positive electrode and the first specific surface area value of the negative electrode; the second specific surface area value is the sum of the second specific surface area value of the positive electrode and the second specific surface area value of the negative electrode.

6. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 1, characterized in that: In the step 1, a plurality of the first lithium-ion batteries have a reference electrode inside; the reference electrode is isolated from the positive electrode and the negative electrode of the first lithium-ion battery by a diaphragm, and the reference electrode is connected to the external circuit of the first lithium-ion battery through a tab.

7. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 1, characterized in that: In the step 1, the positive electrode of the first lithium-ion batteries is any one of lithium nickel cobalt manganese oxide and its derivatives, lithium nickel cobalt aluminum oxide and its derivatives.

8. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 1, characterized in that: In the step 1, the negative electrodes of the first lithium-ion batteries include at least one of silicon-based materials and their derivatives, and graphite materials and their derivatives.

9. The in-situ evaluation method for mechanical properties of a lithium-ion battery according to claim 1, characterized in that: In step 2, the cycle times are spaced between 20 and 200 times.

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