In-situ measurement method for tortuosity of battery

Abstract

The invention relates to the technical field of lithium ion battery measurement, and provides a battery tortuosity in-situ measurement method, which comprises the following steps: obtaining first pole pieces, and combining the first pole pieces into a symmetrical battery; performing an electrochemical impedance spectroscopy (EIS) test on the symmetric battery to obtain a Nyquist map of the symmetric battery, and determining the anode tortuosity of the symmetric battery according to the Nyquist map; obtaining a second pole piece, and combining the first pole piece and the second pole piece into a total battery; the polarity of the second pole piece is opposite to that of the first pole piece; adjusting the state of charge of the total battery to a preset state, and performing an electrochemical impedance spectroscopy (EIS) test on the adjusted total battery based on at least three different ambient temperatures to obtain an electrochemical impedance spectroscopy of the adjusted total battery; optimizing the electrochemical impedance spectrum to obtain the total impedance of the whole battery; the total impedance comprises the sum of interface impedances of the positive electrode and the negative electrode of the total battery and the sum of liquid phase impedances; and determining the negative electrode tortuosity of the total battery according to the total impedance and the positive electrode tortuosity of the symmetrical battery.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery measurement, and in particular to an in-situ measurement method for battery tortuosity. Background Art

[0002] Lithium-ion batteries occupy an important position in the current market due to their wide application, and with the growing demand for fast charging performance, thick electrode design has become a core trend in battery design. The performance of thick electrodes is mainly affected by their tortuosity. The lower the tortuosity, the smaller the internal resistance of the electrode, and the better the fast charging performance of the battery.

[0003] However, in the related art, when measuring the battery tortuosity, the influence of the state of charge on the negative electrode tortuosity is often not fully considered, or the whole battery needs to be disassembled to obtain the electrode pieces with different states of charge for testing. This method may damage the sample during the disassembly process, thus affecting the accuracy of the test results. Therefore, how to accurately measure the battery tortuosity with different states of charge has become an urgent problem to be solved. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention proposes an in-situ measurement method for battery tortuosity, using full batteries with different polarities to perform electrochemical impedance spectroscopy tests at different ambient temperatures, and using symmetrical batteries with the same polarity to perform electrochemical impedance spectroscopy tests at room temperature, and using the data obtained from the two test conditions to determine the tortuosity of the target electrode at different charge states, effectively realizing the measurement of battery tortuosity at different charge states, which is of great significance for accurately evaluating and optimizing electrode performance.

[0005] To achieve the above-mentioned purpose, the first embodiment of the present invention proposes an in-situ measurement method of battery tortuosity, including: obtaining a first pole piece, combining the first pole pieces into a symmetrical battery; performing an electrochemical impedance spectroscopy (EIS) test on the symmetrical battery to obtain the Nyquist diagram of the symmetrical battery, and determining the positive electrode tortuosity of the symmetrical battery according to the Nyquist diagram; obtaining a second pole piece, combining the first pole piece and the second pole piece into a full battery; wherein the second pole piece has an opposite polarity to the first pole piece; adjusting the charge state of the full battery to a preset state, performing an electrochemical impedance spectroscopy (EIS) test on the adjusted full battery based on at least three different ambient temperatures, and obtaining the electrochemical impedance spectrum of the adjusted full battery; optimizing the electrochemical impedance spectrum to obtain the total impedance of the full battery; wherein the total impedance includes the sum of the interface impedances of the positive electrode of the full battery and the negative electrode of the full battery and the sum of the liquid phase impedances; determining the negative electrode tortuosity of the full battery according to the total impedance and the positive electrode tortuosity of the symmetrical battery.

[0006] In addition, the in-situ measurement method of battery tortuosity according to the above embodiment of the present invention may also have the following additional technical features:

[0007] According to some embodiments of the present invention, the positive electrode tortuosity of the symmetrical battery is determined based on the Nyquist diagram, including: extending the low-frequency line segment in the Nyquist diagram to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, to obtain the first intersection coordinate; extending the high-frequency line segment in the Nyquist diagram to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, to obtain the second intersection coordinate; calculating the difference between the second intersection coordinate and the first intersection coordinate, and determining the positive electrode tortuosity of the symmetrical battery based on the difference.

[0008] According to some embodiments of the present invention, determining the positive electrode tortuosity of the symmetrical battery according to the difference includes:

[0009]

[0010] Among them, τ pos R represents the positive electrode tortuosity of the symmetrical battery; ion_pos is three times the difference between the coordinates of the second intersection point and the coordinates of the first intersection point, representing the liquid phase impedance of the symmetrical battery; S pos Represents the effective electrode area of ​​the symmetrical battery, in m 2 ; κ represents the conductivity of the electrolyte at ambient temperature, in S / m; ε pos Indicates the positive electrode porosity; L pos Represents the coating thickness of a symmetrical cell, in m.

[0011] According to some embodiments of the present invention, the electrochemical impedance spectrum is optimized to obtain the objective function in the optimization process of the total impedance of the full battery:

[0012]

[0013] Among them, Object represents the objective function, and the objective function takes the minimum value during the optimization process; Z exp_real represents the real impedance obtained from the full battery test, Z real The analytical solution of the real impedance of the full battery, Z exp_imag represents the imaginary impedance obtained from the full battery test, Z imag represents the analytical solution of the imaginary impedance of the full battery, k represents the amount of electrochemical impedance spectrum data for each ambient temperature, and j represents the test frequency.

[0014] According to some embodiments of the present invention, the total impedance of the full battery is:

[0015] Z=Z ohm +Z pos +Z neg

[0016] Where Z represents the total impedance of the whole battery, Zohm represents the ohmic impedance of the full battery, Z pos represents the positive electrode impedance of the full battery, Z neg Represents the negative electrode impedance of the full battery.

[0017] According to some embodiments of the present invention, the analytical solution of the positive electrode impedance and the analytical solution of the negative electrode impedance of the full battery are expressed as:

[0018]

[0019] Among them, Z pos represents the analytical solution of the positive electrode impedance of the full battery; X 1pos It represents the liquid phase impedance of the positive electrode of the whole battery, in Ω / m; X 2pos It represents the solid phase impedance of the positive electrode of the whole battery, in Ω / m; L pos Indicates the coating thickness of the positive electrode of the full battery, in m; Z neg represents the analytical solution of the negative electrode impedance of the full battery; X 1neg It represents the liquid phase impedance of the negative electrode of the whole battery, in Ω / m; X 2neg Represents the solid phase impedance of the negative electrode of the whole battery, in Ω / m; L neg Represents the coating thickness of the negative electrode of the whole battery, in m.

[0020] According to some embodiments of the present invention, the liquid phase impedance of the positive electrode of the full battery and the liquid phase impedance of the negative electrode of the full battery are expressed as:

[0021]

[0022] Among them, ρ pos is the solid phase resistivity of the positive electrode of the whole battery, in Ω·m; ρ neg is the solid phase resistivity of the negative electrode of the whole battery, in Ω·m; τ neg is the negative electrode tortuosity of the whole battery; ε neg is the porosity of the negative electrode of the whole battery; S pos is the effective electrode area of ​​the positive electrode of the whole battery, in m 2 ; S neg is the effective area of ​​the negative electrode of the whole battery, in m 2 .

[0023] According to some embodiments of the present invention, the intermediate variables of the analytical solution of the positive electrode impedance of the full battery and the intermediate variables of the analytical solution of the negative electrode impedance are expressed as:

[0024]

[0025] Among them, λ pos is the intermediate variable of the analytical solution of the positive electrode impedance of the full battery; pos is the interfacial impedance of the positive electrode of the whole battery;neg is the intermediate variable of the analytical solution of the negative electrode impedance of the full battery; neg is the interfacial impedance of the negative electrode of the full battery.

[0026] According to some embodiments of the present invention, the interface impedance of the positive electrode and the interface impedance of the negative electrode of the full battery are expressed as:

[0027]

[0028] Among them, ξ pos is the interfacial impedance of the positive electrode of the whole battery; R ctpos is the interfacial resistance of the positive electrode of the whole battery, in Ω·m; j is the imaginary unit; ω is the angular velocity; P pos is the non-ideal capacitance coefficient of the positive electrode of the full battery; C dlpos is the interfacial capacitance of the positive electrode of the whole battery, in F / m; S pos is the area of ​​the positive electrode material of the whole battery, in m 2 ξ neg is the interfacial impedance of the negative electrode of the whole battery; R ctneg is the interfacial resistance of the negative electrode of the whole battery, in Ω·m; j is the imaginary unit; ω is the angular velocity; P neg is the non-ideal capacitance coefficient of the negative electrode of the whole battery; C dlneg is the interfacial capacitance of the negative electrode of the whole battery, in F / m; S neg is the area of ​​the negative electrode material of the whole battery, in m 2 .

[0029] According to some embodiments of the present invention, the method of optimizing the electrochemical impedance spectroscopy includes one or more of a heuristic algorithm, a least squares method, or a conjugate gradient method.

[0030] From the above, it can be seen that the present invention provides an in-situ measurement method for battery tortuosity, which performs in-situ electrochemical impedance spectroscopy testing on the whole battery to obtain the positive / negative electrode tortuosity, without disassembling the battery to make a negative electrode symmetrical battery, and the operation is simple and feasible, which reduces the damage to the battery electrode state. Furthermore, the electrochemical impedance spectroscopy test data of the whole battery at multiple ambient temperatures are used for synchronous optimization, and the two impedances are separated based on the activation energy difference between the interface impedance and the liquid phase impedance. Combined with the known positive / negative electrode tortuosity, the negative / positive electrode tortuosity is obtained. At the same time, the full battery in-situ test can also be used to quantify the influence of factors such as charge state on the tortuosity, thereby improving the accuracy of the battery tortuosity test and providing an accurate reference for optimizing battery performance.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 A flow chart of an in-situ measurement method for battery tortuosity provided in an embodiment of the present invention.

[0034] Figure 2 The Nyquist diagram of the ternary-graphite system positive electrode symmetrical battery at 25°C of Example 1 provided in the embodiments of the present invention.

[0035] Figure 3 This is a graph of the electrochemical impedance spectroscopy optimization results of the ternary-graphite system full battery of Example 1 provided in the embodiments of the present invention under different temperature conditions.

[0036] Figure 4 The Nyquist diagram of the lithium iron carbonate-graphite system positive electrode symmetrical battery at 25°C of Example 2 provided in the embodiments of the present invention.

[0037] Figure 5 This is a graph of the electrochemical impedance spectroscopy optimization results of the lithium iron carbonate-graphite system full battery of Example 2 provided in the embodiments of the present invention under different temperature conditions.

[0038] Figure 6 The Nyquist diagram of the ternary-graphite system negative electrode symmetrical battery at 25°C of Comparative Example 1 provided in the embodiments of the present invention. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0040] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0041] As described in the background technology section, lithium-ion batteries play an increasingly important role in modern society due to their advantages such as high energy density, long service life, good fast charging capability and low cost. Especially in the use scenario where fast charging is required, it has become mainstream to design lithium-ion batteries in the form of thick electrodes. Therefore, the requirements for measuring the tortuosity of the battery are gradually increasing. In the related art, the measurement of tortuosity is generally carried out by making symmetrical batteries to measure the tortuosity of the electrodes. However, directly measuring the tortuosity of symmetrical batteries with fresh pole pieces cannot take into account the influence of the state of charge on the tortuosity of the negative electrode, or it is necessary to disassemble the entire battery to obtain pole pieces with different states of charge, which may damage the battery sample and affect the accuracy of the test. Therefore, how to effectively and accurately measure the tortuosity of batteries under different states of charge has become a technical problem that needs to be overcome.

[0042] In the process of implementing the present invention, the applicant discovered that the tortuosity of the battery can be calculated by using the electrochemical impedance spectrum of the symmetrical battery and the electrochemical impedance spectrum of the full battery: the tortuosity of the positive electrode / negative electrode is obtained by performing an electrochemical impedance spectrum test on the positive electrode / negative electrode symmetrical battery, and further, the electrochemical impedance spectrum of the full battery is tested under different temperature conditions, and the tortuosity of the negative electrode / positive electrode is obtained by combining the measured positive electrode / negative electrode tortuosity. According to the in-situ measurement method of battery tortuosity provided by the present invention, the tortuosity of the battery at different charge states can be obtained without disassembling the full battery.

[0043] The technical solution of the present invention is further described in detail below through specific embodiments.

[0044] refer to Figure 1 , which is an in-situ measurement method of battery tortuosity provided by an embodiment of the present invention.

[0045] Step S101, obtaining a first pole piece, and combining the first pole pieces into a symmetrical battery.

[0046] Specifically, a symmetrical battery is a battery structure with two identical working electrodes. In the embodiment of the present invention, the first electrode is preferably a positive electrode. Exemplarily, a symmetrical battery can be made according to a specific method. First, two electrodes of the same polarity are placed opposite to each other, separated by a layer of diaphragm, and the electrode and the diaphragm are fixed into a battery cell; secondly, the battery cell is loaded into a battery shell, and an appropriate amount of electrolyte is injected to ensure that the electrochemical reaction inside the battery can proceed smoothly; finally, the battery shell is sealed and packaged to obtain a symmetrical battery sample to be tested. Step S102, perform an electrochemical impedance spectroscopy (EIS) test on the symmetrical battery to obtain the Nyquist diagram of the symmetrical battery, and determine the positive electrode tortuosity of the symmetrical battery according to the Nyquist diagram;

[0047] Among them, electrochemical impedance spectroscopy (EIS) is also called AC impedance. EIS test is an electrochemical measurement method that uses a small-amplitude sinusoidal potential (or current) as a disturbance signal. The Nyquist plot is further obtained based on the EIS test.

[0048] The Nyquist plot can intuitively show the relationship between the real and imaginary parts of the impedance. The high-frequency region of the Nyquist plot usually appears as a smaller arc, which is related to the ohmic resistance and charge transfer resistance of the battery; the medium-frequency region appears as a larger arc, which is usually related to the double-layer capacitance and charge transfer resistance of the electrode / electrolyte interface; the low-frequency region usually appears as a diagonal line, which is related to the diffusion process inside the electrode.

[0049] Specifically, an electrochemical impedance spectroscopy (EIS) test is performed on the symmetrical battery at a specific temperature, and a Nyquist diagram of the symmetrical battery at the corresponding specific temperature is further obtained, and the positive electrode tortuosity of the symmetrical battery is calculated according to the Nyquist diagram. The specific temperature is preferably room temperature 25° C. in the embodiment of the present invention.

[0050] As an optional embodiment, determining the positive electrode tortuosity of the symmetrical battery according to the Nyquist diagram includes: extending the low-frequency line segment in the Nyquist diagram to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, to obtain the first intersection coordinate; extending the high-frequency line segment in the Nyquist diagram to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, to obtain the second intersection coordinate; calculating the difference between the second intersection coordinate and the first intersection coordinate, and determining the positive electrode tortuosity of the symmetrical battery according to the difference.

[0051] Specifically, the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located represents the real component of the impedance, that is, the real part of the impedance. The low-frequency line segment in the Nyquist diagram is extended to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, and the first intersection coordinate A (a, 0) is obtained. Further, the high-frequency line segment in the Nyquist diagram is extended to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, and the second intersection coordinate B (b, 0) is obtained; the electrode liquid phase impedance value is three times the difference between the coordinate values ​​of the first intersection on the left and the second intersection, that is, R ion_pos =3(ab). Based on the relationship between the electrode liquid phase impedance and tortuosity, the positive electrode tortuosity of the symmetrical battery can be further calculated.

[0052] It should be noted that the liquid phase impedance of the battery is the resistance generated by the movement of ions in the electrolyte inside the battery. The liquid phase impedance has an important influence on performance indicators such as battery capacity, charge and discharge efficiency, and cycle life, and is also an important component of the battery's internal impedance.

[0053] As an optional embodiment, determining the positive electrode tortuosity of the symmetrical battery according to the difference includes:

[0054]

[0055] Among them, τ pos R represents the positive electrode tortuosity of the symmetrical battery; ion_pos is three times the difference between the coordinates of the second intersection point and the coordinates of the first intersection point, representing the liquid phase impedance of the symmetrical battery; S pos Represents the effective electrode area of ​​the symmetrical battery, in m 2 ; κ represents the conductivity of the electrolyte at ambient temperature, in S / m; ε pos Indicates the positive electrode porosity; L pos Represents the coating thickness of a symmetrical cell, in m.

[0056] It should be noted that κ represents the conductivity of the electrolyte at the current test ambient temperature. In this embodiment, the ambient temperature is preferably 25°C.

[0057] Specifically, the liquid phase impedance R of the symmetrical battery is ion_pos , the effective electrode area S of the symmetrical battery pos , the conductivity κ of the electrolyte at ambient temperature, the porosity ε pos , coating thickness L for symmetrical cells pos Substituting into the solution formula of the positive electrode tortuosity of the symmetrical battery, the positive electrode tortuosity of the symmetrical battery at the current ambient temperature can be obtained. Among them, the effective electrode area S of the symmetrical battery pos , the conductivity κ of the electrolyte at ambient temperature, the porosity ε pos , coating thickness L for symmetrical cellspos are all known parameters.

[0058] Step S103, obtaining a second pole piece, and combining the first pole piece and the second pole piece into a full battery; wherein the polarity of the second pole piece is opposite to that of the first pole piece.

[0059] Specifically, the first electrode is preferably a positive electrode, and the second electrode has the opposite polarity to the first electrode, that is, the second electrode is preferably a negative electrode. The positive electrode, the negative electrode and the separator are wound or stacked in sequence to form a battery cell, and loaded into a battery shell; then, the electrolyte is injected, and the stability of the internal environment of the battery is ensured by sealing and packaging; finally, the battery cell is electrochemically treated to enable the battery to have discharge capacity and ensure performance consistency, thereby completing the production of a full battery as a full battery to be tested. It should be noted that the difference between a full battery and a symmetrical battery is that the electrode sheets of a symmetrical battery have the same polarity, which can be positive-positive or negative-negative, while the electrode sheets of a full battery have a single polarity, that is, the structure of the full battery is positive-negative.

[0060] Step S104, adjusting the state of charge of the full battery to a preset state, performing an electrochemical impedance spectroscopy (EIS) test on the adjusted full battery based on at least three different ambient temperatures, and obtaining an electrochemical impedance spectrum of the adjusted full battery.

[0061] Specifically, the battery's state of charge (SOC) is used to describe the measure of the remaining power in the battery, reflecting the ratio of the power that the battery can currently provide to the power that it can provide when fully charged, usually expressed as a percentage (%). When SOC = 0, it means that the battery is fully discharged; when SOC = 1, it means that the battery is fully charged. The preset state of the full battery's state of charge can be adjusted according to different test requirements, and the impact of the state of charge on the battery tortuosity can be quantified.

[0062] Specifically, the battery has different activation energies under different temperature conditions. Since the interfacial impedance involves the transfer and conversion process of charge on the interface, the activation energy of the interfacial impedance is usually higher, while the liquid phase impedance involves the transfer of ions in the solution. Compared with the interfacial impedance, the activation energy of the liquid phase impedance is usually lower. Therefore, since the activation energies of the interfacial impedance and the liquid phase impedance are different when the temperature changes, that is, the response to temperature is different, the impedance change trend and amplitude at different temperatures can be obtained by analyzing the electrochemical impedance spectroscopy test data at different temperatures, and the interfacial impedance and the liquid phase impedance can be distinguished, thereby achieving an effective separation of the interfacial impedance and the liquid phase impedance. Regarding the electrochemical impedance spectroscopy test at different temperatures, it is necessary to combine the specific embodiments to explain it later.

[0063] It should be noted that the interfacial impedance mainly reflects the interface characteristics between the electrochemical reaction inside the battery and the external circuit. Its size depends on factors such as the chemical reaction rate inside the battery, the characteristics of the electrode material, the concentration and temperature of the electrolyte, and the contact conditions between the electrolyte and the electrode.

[0064] By adjusting the charge state of the whole battery to a preset state, further performing electrochemical impedance spectroscopy (EIS) tests on the whole battery based on three different ambient temperatures, and testing the electrochemical impedance spectrum of the whole battery under different temperature conditions, it is possible to optimize the electrochemical impedance spectrum of the whole battery, make the measurement results more accurate, and obtain an optimized and adjusted electrochemical impedance spectrum of the whole battery.

[0065] Step S105, optimizing the electrochemical impedance spectrum to obtain the total impedance of the whole battery; wherein the total impedance includes the sum of the interface impedances of the positive electrode of the whole battery and the negative electrode of the whole battery and the sum of the liquid phase impedance.

[0066] Specifically, the interfacial impedance of the positive electrode of the whole battery is the resistance between the positive electrode of the battery and the electrolyte or other related interfaces, including chemical resistance and charge transfer resistance. Among them, chemical resistance is the resistance generated by the chemical reaction between the positive electrode material and the electrolyte, while charge transfer resistance is the resistance generated by the transfer process of electrons and ions at the interface. Similarly, the interfacial impedance of the negative electrode of the whole battery is the resistance between the negative electrode of the battery and the electrolyte or other related interfaces, also including chemical resistance and charge transfer resistance. The interfacial impedance between the positive and negative electrodes is an important component of the internal impedance of the battery and has a significant impact on the battery life and health.

[0067] The sum of the interfacial impedances of the positive and negative electrodes of the battery and the sum of the liquid phase impedance of the battery together constitute the total impedance value of the whole battery. By further optimizing the electrochemical impedance spectrum of the whole battery, an accurate total impedance value of the whole battery can be obtained.

[0068] As an optional embodiment, the electrochemical impedance spectrum is optimized to obtain the objective function in the optimization process of the total impedance of the full battery:

[0069]

[0070] Among them, Object represents the objective function, and the objective function takes the minimum value during the optimization process; Z exp_real represents the real impedance obtained from the full battery test, Z real The analytical solution of the real impedance of the full battery, Z exp_imag represents the imaginary impedance obtained from the full battery test, Z imag represents the analytical solution of the imaginary impedance of the full battery, k represents the amount of electrochemical impedance spectrum data for each ambient temperature, and j represents the test frequency.

[0071] It should be noted that Object is the objective function, which represents the impedance error of the optimization target, that is, the impedance error of the whole battery, and takes the minimum value during the optimization process; the test frequency j represents the number of test temperatures, that is, testing under several temperature conditions.

[0072] It should be noted that the real impedance and imaginary impedance of the whole battery are important parameters for evaluating battery performance. Among them, the real impedance is also called the resistance part. The battery's resistance to alternating current mainly comes from the ohmic resistance, electrolyte resistance, electrode material resistance, etc. inside the battery. In the full battery test, the value of the real impedance can directly reflect the internal resistance of the battery and is one of the important indicators for evaluating the performance of the battery. When the battery is in different states of charge, its internal structure and chemical reaction state will change, resulting in changes in the real impedance; the imaginary impedance is also called the capacitance or inductance part, which reflects the battery's response speed to alternating current, that is, the distribution and migration of charges and ions inside the battery. In the full battery test, the value of the imaginary impedance is related to the capacitance effect and inductance effect of the battery.

[0073] As an optional embodiment, the method of optimizing the electrochemical impedance spectroscopy includes one or more of a heuristic algorithm, a least squares method or a conjugate gradient method.

[0074] Specifically, according to the objective function in the optimization process of the total impedance of the whole battery, the electrochemical impedance spectrum of the whole battery is optimized. The objective function can be based on one or more of the heuristic algorithm, the least squares method or the conjugate gradient method. The objective function can be accurately optimized through a variety of calculation methods to ensure that the optimal solution of the objective function matches the electrochemical impedance spectrum, thereby further improving the accuracy of the test.

[0075] As an optional embodiment, the total impedance of the full battery is:

[0076] Z=Z ohm +Z pos +Z neg

[0077] Where Z represents the total impedance of the whole battery, Z ohm represents the ohmic impedance of the full battery, Z pos represents the positive electrode impedance of the full battery, Z neg Represents the negative electrode impedance of the full battery.

[0078] It should be noted that the total impedance of the whole battery includes ohmic impedance, positive electrode impedance and negative electrode impedance. Among them, ohmic impedance is mainly composed of ionic resistance and electronic resistance. Ionic resistance is the resistance encountered by lithium ions in the transfer of the battery, and electronic resistance is the resistance encountered by electron transfer. Liquid phase impedance is the specific manifestation of the ionic resistance part of ohmic impedance.

[0079] Step S106, determining the negative electrode tortuosity of the full battery according to the total impedance and the positive electrode tortuosity of the symmetrical battery.

[0080] Specifically, the negative electrode tortuosity of the full battery is the main object to be solved by the in-situ measurement method of the battery tortuosity provided by the present invention. According to the formula provided in the following embodiment, the unique solution of the negative electrode tortuosity of the full battery can be obtained:

[0081] As an optional embodiment, the analytical solution of the positive electrode impedance and the analytical solution of the negative electrode impedance of the full battery are expressed as:

[0082]

[0083] Among them, Z pos represents the analytical solution of the positive electrode impedance of the full battery; X 1pos It represents the liquid phase impedance of the positive electrode of the whole battery, in Ω / m; X 2pos It represents the solid phase impedance of the positive electrode of the whole battery, in Ω / m; L pos Indicates the coating thickness of the positive electrode of the full battery, in m; Z neg represents the analytical solution of the negative electrode impedance of the full battery; X 1neg It represents the liquid phase impedance of the negative electrode of the whole battery, in Ω / m; X 2neg Represents the solid phase impedance of the negative electrode of the whole battery, in Ω / m; L neg Represents the coating thickness of the negative electrode of the whole battery, in m.

[0084] It should be noted that the solid phase impedance of the whole battery reflects the hindering effect of the solid phase material (such as electrode material) inside the battery on the diffusion of lithium ions, and is a known parameter in the embodiment of the present invention. The size of the solid phase impedance directly affects the charge and discharge performance and cycle life of the battery. A smaller solid phase impedance means that the diffusion rate of lithium ions in the electrode material is faster and the charge and discharge performance of the battery is better; a larger solid phase impedance will cause heat to be generated inside the battery, reducing the efficiency and safety of the battery.

[0085] As an optional embodiment, the liquid phase impedance of the positive electrode of the full battery and the liquid phase impedance of the negative electrode of the full battery are expressed as:

[0086]

[0087] Among them, ρ pos is the solid phase resistivity of the positive electrode of the whole battery, in Ω·m; ρ neg is the solid phase resistivity of the negative electrode of the whole battery, in Ω·m; τ neg is the negative electrode tortuosity of the whole battery; ε neg is the porosity of the negative electrode of the whole battery; S pos is the effective electrode area of ​​the positive electrode of the whole battery, in m 2; S neg is the effective area of ​​the negative electrode of the whole battery, in m 2 .

[0088] As an optional embodiment, the intermediate variables of the analytical solution of the positive electrode impedance of the full battery and the intermediate variables of the analytical solution of the negative electrode impedance are expressed as:

[0089]

[0090] Among them, λ pos is the intermediate variable of the analytical solution of the positive electrode impedance of the full battery; pos is the interfacial impedance of the positive electrode of the whole battery; neg is the intermediate variable of the analytical solution of the negative electrode impedance of the full battery; neg is the interfacial impedance of the negative electrode of the full battery.

[0091] As an optional embodiment, the interface impedance of the positive electrode and the interface impedance of the negative electrode of the full battery are expressed as:

[0092]

[0093] Among them, ξ pos is the interfacial impedance of the positive electrode of the whole battery; R ctpos is the interfacial resistance of the positive electrode of the whole battery, in Ω·m; j is the imaginary unit; ω is the angular velocity; P pos is the non-ideal capacitance coefficient of the positive electrode of the full battery; C dlpos is the interfacial capacitance of the positive electrode of the whole battery, in F / m; S pos is the area of ​​the positive electrode material of the whole battery, in m 2 ξ neg is the interfacial impedance of the negative electrode of the whole battery; R ctneg is the interfacial resistance of the negative electrode of the whole battery, in Ω·m; j is the imaginary unit; ω is the angular velocity; P neg is the non-ideal capacitance coefficient of the negative electrode of the whole battery; C dleng is the interfacial capacitance of the negative electrode of the whole battery, in F / m; S neg is the area of ​​the negative electrode material of the whole battery, in m 2 .

[0094] It should be noted that among the parameters in the above embodiment, the parameter to be optimized is the tortuosity of the negative electrode of the full battery τ neg , the interface resistance R of the positive electrode of the full battery ctpos , the interface resistance R of the negative electrode of the full battery ctneg , the interfacial capacitance C of the positive electrode of the full battery dlpos , the interface capacitance C of the negative electrode of the full battery dleng , the non-ideal capacitance coefficient P of the positive electrode of the full battery pos , the non-ideal capacitance coefficient P of the negative electrode of the full batteryneg , and the ohmic impedance Z of the full battery ohm ; Input parameter is the solid phase resistivity ρ of the positive electrode of the whole battery pos 、The solid phase resistivity ρ of the negative electrode of the whole battery neg , Full battery positive electrode tortuosity (positive electrode tortuosity of symmetrical battery) τ pos 、Full battery positive electrode effective plate area S pos 、Full battery negative electrode effective plate area S neg 、Porosity of negative electrode of full battery ε neg 、Full battery positive electrode porosity battery ε pos 、Coating thickness L of the positive electrode of the full battery pos 、Coating thickness L of the negative electrode of the whole battery neg , and the conductivity κ of the electrolyte at ambient temperature.

[0095] Specifically, among the parameters of the above embodiments, except for the positive electrode tortuosity of the full battery (the positive electrode tortuosity of the symmetrical battery) τ pos In addition, the other parameters are the interface resistance R of the positive electrode of the full battery ctpos , the interfacial resistance R of the negative electrode of the full battery ctneg , the interfacial capacitance C of the positive electrode of the full battery dlpos , the interface capacitance C of the negative electrode of the full battery dleng , the non-ideal capacitance coefficient P of the positive electrode of the full battery pos , the non-ideal capacitance coefficient P of the negative electrode of the full battery neg , and the ohmic impedance Z of the full battery ohm 、The solid phase resistivity ρ of the positive electrode of the whole battery pos 、The solid phase resistivity ρ of the negative electrode of the whole battery neg , Full battery positive electrode tortuosity (positive electrode tortuosity of symmetrical battery) τ pos 、Full battery positive electrode effective plate area S pos 、Full battery negative electrode effective plate area S neg 、Porosity of negative electrode of full battery ε neg 、Full battery positive electrode porosity battery ε pos 、Coating thickness L of the positive electrode of the full battery pos 、Coating thickness L of the negative electrode of the whole battery neg The conductivity κ of the electrolyte at ambient temperature and the conductivity κ of the electrolyte at ambient temperature are known parameters that can be directly measured or given in the test plan.

[0096] Specifically, since the total impedance of the whole battery is optimized under multiple temperature conditions, it is generally based on the difference in activation energy between the interface impedance and the liquid phase impedance, and the two are split and optimized to ensure that the sum of the cross-sectional impedances of the positive and negative electrodes and the sum of the liquid phase impedances of the optimized whole battery are accurate.

[0097] It should be noted that by optimizing the total impedance of the whole battery under multiple temperature conditions, it is impossible to specifically distinguish the interface impedance and liquid phase impedance of the positive or negative electrode of the whole battery.

[0098] It should be noted that, in the above embodiment, the positive electrode tortuosity τ of the symmetrical battery has been obtained. pos That is, the positive electrode tortuosity of the whole battery. The thickness of the positive electrode coating of the whole battery is basically independent of the state of charge. Therefore, the tortuosity of the positive electrode can be approximated as a constant, and the accurate tortuosity of the negative electrode can be further obtained.

[0099] In combination with the above, the parameter to be optimized in the present invention is the negative electrode tortuosity of the full battery neg The result of is the only solution and has practical significance, while the optimization results of the remaining parameters to be optimized are meaningless in themselves and only participate in the optimization process to improve the optimization accuracy.

[0100] Optionally, the method provided by the present invention is further described in detail in combination with the following multiple embodiments.

[0101] Example 1: The positive electrode sheet is a ternary-graphite system as the research object:

[0102] Step S1: obtaining fresh positive electrode sheets and further assembling them into symmetrical batteries;

[0103] Step S2: performing an electrochemical impedance spectroscopy test on the positive electrode symmetrical battery at 25°C;

[0104] Among them, the input and output parameters of the electrochemical impedance spectroscopy test of the positive electrode symmetrical battery are shown in Table 1:

[0105]

[0106]

[0107] Table 1

[0108] Specifically, the test frequency range is 1 MHz-0.01 Hz, the voltage excitation is 10 mV, and the corresponding Nyquist plot is obtained.

[0109] refer to Figure 2 , which is the Nyquist diagram of the ternary-graphite system positive electrode symmetrical battery at 25°C according to Example 1 provided in an embodiment of the present invention.

[0110] The high-frequency line segment is marked as 1, and the extended line of the low-frequency line segment is marked as 2.

[0111] Furthermore, the Nyquist diagram obtained by the test is analyzed and processed, the low-frequency line segment is extended, and the first intersection coordinate A1 (a1, 0) is obtained by intersecting the x-axis of the two-dimensional coordinate system where the Nyquist diagram is located. The coordinate of the intersection of the high-frequency line segment and the x-axis of the two-dimensional coordinate system where the Nyquist diagram is located is set as the second intersection coordinate B1 (b1, 0), and the liquid phase impedance R of the symmetrical battery can be obtained. ion_pos =3(a1-b1).

[0112] Further, according to the liquid phase impedance R of the symmetrical battery ion_pos , the effective electrode area S of the symmetrical battery pos , the conductivity κ of the electrolyte at ambient temperature, the porosity ε pos , coating thickness L for symmetrical cells pos Substituting the tortuosity of the positive electrode of the symmetrical battery into the solution formula, the tortuosity of the positive electrode of the symmetrical battery at 25°C is obtained to be 2.94.

[0113] Step S3: Obtain a full battery;

[0114] Specifically, a full battery is a battery that has been assembled and contains pole pieces with opposite polarities.

[0115] Step S4: performing an electrochemical impedance spectroscopy test on the full battery;

[0116] Specifically, the state of charge of the full battery was adjusted to 50%, and then the electrochemical impedance spectroscopy test was performed on the full battery at temperatures of 15°C, 25°C and 35°C, respectively, with a test frequency range of 1MHz-0.01Hz and a voltage excitation of 10mV.

[0117] Step S5: Optimizing the electrochemical impedance spectrum of the full battery to obtain the total impedance of the full battery;

[0118] Specifically, according to the optimization calculation formula of the method of the present invention, the electrochemical impedance spectrum of the full battery is optimized to obtain the corresponding optimization result of the electrochemical impedance spectrum of the full battery.

[0119] refer to Figure 3 , which is a graph of the electrochemical impedance spectroscopy optimization results of the ternary-graphite system full battery of Example 1 provided in an embodiment of the present invention under different temperature conditions.

[0120] Step S6: Determine the negative electrode tortuosity of the full battery according to the total impedance and the positive electrode tortuosity of the symmetrical battery.

[0121] Among them, the input and output parameters of the optimization process are shown in Table 2:

[0122]

[0123] Table 2

[0124] Specifically, according to the optimization calculation formula of the method of the present invention, combined with the total impedance optimization of the whole battery, the negative electrode tortuosity of the whole battery is further calculated, and the negative electrode tortuosity of the whole battery when the state of charge is 50% is obtained to be 6.33.

[0125] Example 2: The positive electrode sheet is based on the lithium iron phosphate-graphite system:

[0126] Step S1, obtaining fresh positive electrode sheets and further assembling them into symmetrical batteries;

[0127] Step S2, performing an electrochemical impedance spectroscopy test on the positive electrode symmetrical battery at 25° C.;

[0128] Among them, the input and output parameters of the electrochemical impedance spectroscopy test of the positive electrode symmetrical battery are shown in Table 3:

[0129]

[0130] Table 3

[0131] Specifically, the test frequency range is 1 MHz-0.01 Hz, the voltage excitation is 10 mV, and the corresponding Nyquist plot is obtained.

[0132] refer to Figure 4 , which is the Nyquist diagram of the lithium iron carbonate-graphite system positive electrode symmetrical battery of Example 2 provided in an embodiment of the present invention at 25°C.

[0133] Among them, the high-frequency line segment is marked as 3, and the extended line of the low-frequency line segment is marked as 4.

[0134] Furthermore, the Nyquist diagram obtained by the test is analyzed and processed, the low-frequency line segment is extended, and the first intersection coordinate A2 (a2, 0) is obtained by intersecting the x-axis of the two-dimensional coordinate system where the Nyquist diagram is located. The coordinate of the intersection of the high-frequency line segment and the x-axis of the two-dimensional coordinate system where the Nyquist diagram is located is set as the second intersection coordinate B2 (b2, 0), and the liquid phase impedance R of the symmetrical battery can be obtained. ion_pos =3(a2-b2).

[0135] Further, according to the liquid phase impedance R of the symmetrical battery ion_pos , the effective electrode area S of the symmetrical battery pos , the conductivity κ of the electrolyte at ambient temperature, the porosity ε pos , coating thickness L for symmetrical cells pos Substituting the tortuosity of the positive electrode of the symmetrical battery into the solution formula, the tortuosity of the positive electrode of the symmetrical battery at 25°C is obtained.

[0136] Step S3, obtaining a full battery;

[0137] Step S4, performing an electrochemical impedance spectroscopy test on the full battery;

[0138] Specifically, the state of charge of the full battery was adjusted to 90%, and electrochemical impedance spectroscopy tests were performed on the full battery at temperatures of 15° C., 25° C., and 35° C., respectively. The test frequency range was 1 MHz-0.01 Hz, and the voltage excitation was 10 mV.

[0139] Step S5, optimizing the electrochemical impedance spectrum of the full battery to obtain the total impedance of the full battery;

[0140] Specifically, according to the optimization calculation formula of the method of the present invention, the electrochemical impedance spectrum of the full battery is optimized to obtain the corresponding optimization result of the electrochemical impedance spectrum of the full battery.

[0141] refer to Figure 5 , which is a graph of electrochemical impedance spectroscopy optimization results of the lithium iron carbonate-graphite system full battery of Example 2 provided in an embodiment of the present invention under different temperature conditions.

[0142] Step S6, determining the negative electrode tortuosity of the full battery according to the total impedance and the positive electrode tortuosity of the symmetrical battery.

[0143] Among them, the input and output parameters of the optimization process are shown in Table 4:

[0144]

[0145]

[0146] Table 4

[0147] Specifically, according to the optimization calculation formula of the method of the present invention, combined with the total impedance optimization of the whole battery, the negative electrode tortuosity of the whole battery is further calculated, and the negative electrode tortuosity of the whole battery when the state of charge is 90% is 6.97.

[0148] It should be noted that in Example 1 and Example 2, the materials used for the negative electrode of the full battery are the same, and further comparative analysis can be performed.

[0149] It should be noted that the state of charge of Example 2 is 90%, compared with the state of charge of 50% in Example 1. The tortuosity of the negative electrode of the whole battery in Example 2 is greater than the tortuosity of the negative electrode of the whole battery in Example 1. This is because the state of charge becomes higher, and the volume of graphite increases at a high state of charge, thereby increasing the distance for lithium ions in the battery electrolyte to bypass the graphite for mass transfer, further increasing the tortuosity of the negative electrode of the whole battery.

[0150] Comparative Example 1:

[0151] Specifically, the parameter input and output for calculating the tortuosity of the negative electrode of the symmetrical battery are shown in Table 5:

[0152]

[0153] Table 5

[0154] Comparative Example 1 The same negative electrode sheet tortuosity as in Example 1 was obtained using the method in the related art, and a fresh negative electrode sheet was used to assemble a symmetrical battery, and an electrochemical impedance spectroscopy test was performed at 25° C. The frequency range was 1 MHz-0.01 Hz, the voltage excitation was 10 Mv, and the corresponding Nyquist plot was obtained.

[0155] refer to Figure 6 , which is the Nyquist diagram of the ternary-graphite system negative electrode symmetrical battery of Comparative Example 1 provided in an embodiment of the present invention at 25°C.

[0156] Among them, the high-frequency line segment is marked as 5, and the extended line of the low-frequency line segment is marked as 6.

[0157] Furthermore, the electrode liquid phase impedance R of the negative electrode symmetrical battery is calculated ion_neg , analyze and process the Nyquist diagram obtained by the test, extend the low-frequency line segment, and intersect the x-axis of the two-dimensional coordinate system where the Nyquist diagram is located to obtain the first intersection coordinate A3 (a3, 0), and set the intersection coordinate of the high-frequency line segment and the x-axis of the two-dimensional coordinate system where the Nyquist diagram is located as the second intersection coordinate B3 (b3, 0), and the liquid phase impedance R of the symmetrical battery can be obtained. ion_pos =3(a3-b3).

[0158] According to the electrode liquid phase impedance R of the negative electrode symmetrical battery ion_neg Calculate the negative electrode tortuosity τ neg :

[0159]

[0160] Among them, S neg is the effective electrode area of ​​the negative electrode symmetrical battery, in m 2 ; ε neg is the negative electrode porosity; L neg Represents the coating thickness of a symmetrical cell, in m.

[0161] According to the method for calculating the negative electrode tortuosity provided in the comparative example, the calculated negative electrode tortuosity is 6.14. Since the symmetrical battery is a fresh negative electrode symmetrical battery, its negative electrode has not been overcharged and discharged, and the porous structure (such as porosity) of the negative electrode plate is different from that of the negative electrode plate at 50% charge state in Example 1, so the tortuosity of the two is different.

[0162] From the above description, it can be seen that the in-situ measurement method of battery tortuosity provided in an embodiment of the present invention, by testing the tortuosity of a fresh electrode piece, further performs electrochemical impedance spectroscopy tests on the whole battery at multiple temperatures, and can measure the negative electrode tortuosity of batteries under different charge states while ensuring that the whole battery is in an in-situ state without being disassembled, thereby improving the authenticity and accuracy of the test, and having a positive impact on accurately evaluating and optimizing electrode performance and building a high-precision simulation model.

[0163] It should be noted that some embodiments of the present invention are described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the above embodiments and still achieve the desired results. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0164] In addition, although the operations of the method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that the operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. On the contrary, the steps depicted in the flow chart can be performed in a different order. Additionally or alternatively, some steps can be omitted, multiple steps can be combined into one step, and / or one step can be decomposed into multiple steps.

[0165] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the embodiments of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0166] Although the spirit and principle of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined to benefit, and this division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the attached claims. The scope of the attached claims conforms to the broadest interpretation, thereby including all such modifications and equivalent structures and functions.

Claims

1. An in-situ measurement method for battery tortuosity, characterized in that: include: Obtaining first pole pieces, and combining the first pole pieces into a symmetrical battery; Performing an electrochemical impedance spectroscopy (EIS) test on the symmetrical battery to obtain a Nyquist plot of the symmetrical battery, and determining the tortuosity of the positive electrode of the symmetrical battery according to the Nyquist plot; Obtaining a second pole piece, and combining the first pole piece and the second pole piece into a full battery; wherein the second pole piece has an opposite polarity to the first pole piece; Adjusting the state of charge of the full battery to a preset state, and performing an electrochemical impedance spectroscopy (EIS) test on the adjusted full battery based on at least three different ambient temperatures to obtain an electrochemical impedance spectroscopy (EIS) of the adjusted full battery; Optimizing the electrochemical impedance spectrum to obtain the total impedance of the full battery; wherein the total impedance includes the sum of the interface impedances of the positive electrode of the full battery and the negative electrode of the full battery and the sum of the liquid phase impedance; The negative electrode tortuosity of the full battery is determined according to the total impedance and the positive electrode tortuosity of the symmetrical battery.

2. The in-situ measurement method of battery tortuosity according to claim 1, characterized in that: Determining the positive electrode tortuosity of the symmetrical battery according to the Nyquist diagram includes: Extending the low-frequency line segment in the Nyquist diagram to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, to obtain the coordinates of the first intersection point; Extending the high-frequency line segment in the Nyquist diagram to intersect with the X-axis of the two-dimensional coordinate system where the Nyquist diagram is located, to obtain the coordinates of the second intersection point; The difference between the coordinates of the second intersection point and the coordinates of the first intersection point is calculated, and the tortuosity of the positive electrode of the symmetrical battery is determined according to the difference.

3. The in-situ measurement method of battery tortuosity according to claim 2, characterized in that: The determining the positive electrode tortuosity of the symmetrical battery according to the difference includes: Among them, τ pos R represents the positive electrode tortuosity of the symmetrical battery; ion_pos is three times the difference between the coordinates of the second intersection point and the coordinates of the first intersection point, representing the liquid phase impedance of the symmetrical battery; S pos Represents the effective electrode area of ​​the symmetrical battery, in m 2 ; κ represents the conductivity of the electrolyte at ambient temperature, in S / m; ε pos Indicates the positive electrode porosity; L pos Represents the coating thickness of a symmetrical cell, in m.

4. The in-situ measurement method of battery tortuosity according to claim 3, characterized in that: The objective function in the process of optimizing the electrochemical impedance spectrum to obtain the total impedance of the full battery is: Among them, Object represents the objective function, and the objective function takes the minimum value during the optimization process; Z exp_real represents the real impedance obtained from the full battery test, Z real The analytical solution of the real impedance of the full battery, Z exp_imag represents the imaginary impedance obtained from the full battery test, Z imag represents the analytical solution of the imaginary impedance of the full battery, k represents the amount of electrochemical impedance spectrum data for each ambient temperature, and j represents the test frequency.

5. The in-situ measurement method of battery tortuosity according to claim 4, characterized in that: The total impedance of the full battery is: Z=Z ohm +Z pos +Z neg Where Z represents the total impedance of the whole battery, Z ohm represents the ohmic impedance of the full battery, Z pos represents the positive electrode impedance of the full battery, Z neg Represents the negative electrode impedance of the full battery.

6. The in-situ measurement method of battery tortuosity according to claim 5, characterized in that: The analytical solutions of the positive electrode impedance and the negative electrode impedance of the full battery are expressed as: Among them, Z pos represents the analytical solution of the positive electrode impedance of the full battery; X 1pos It represents the liquid phase impedance of the positive electrode of the whole battery, in Ω / m; X 2pos It represents the solid phase impedance of the positive electrode of the whole battery, in Ω / m; L pos Indicates the coating thickness of the positive electrode of the full battery, in m; Z neg represents the analytical solution of the negative electrode impedance of the full battery; X 1neg It represents the liquid phase impedance of the negative electrode of the whole battery, in Ω / m; X 2neg Represents the solid phase impedance of the negative electrode of the whole battery, in Ω / m; L neg Represents the coating thickness of the negative electrode of the whole battery, in m.

7. The in-situ measurement method of battery tortuosity according to claim 6, characterized in that: The liquid phase impedance of the positive electrode of the full battery and the liquid phase impedance of the negative electrode of the full battery are expressed as: Among them, ρ pos is the solid phase resistivity of the positive electrode of the whole battery, in Ω·m; ρ neg is the solid phase resistivity of the negative electrode of the whole battery, in Ω·m; τ neg is the negative electrode tortuosity of the whole battery; ε neg is the porosity of the negative electrode of the whole battery; S pos is the effective electrode area of ​​the positive electrode of the whole battery, in m 2 ; S neg is the effective area of ​​the negative electrode of the whole battery, in m 2 .

8. The in-situ measurement method of battery tortuosity according to claim 7, characterized in that: The intermediate variables of the analytical solution of the positive electrode impedance of the full battery and the intermediate variables of the analytical solution of the negative electrode impedance are expressed as: Among them, λ pos is the intermediate variable of the analytical solution of the positive electrode impedance of the full battery; pos is the interfacial impedance of the positive electrode of the whole battery; neg is the intermediate variable of the analytical solution of the negative electrode impedance of the full battery; neg is the interfacial impedance of the negative electrode of the full battery.

9. The in-situ measurement method of battery tortuosity according to claim 8, characterized in that: The interfacial impedance of the positive electrode and the interfacial impedance of the negative electrode of the full battery are expressed as: Among them, ξ pos is the interfacial impedance of the positive electrode of the whole battery; R ctpos is the interfacial resistance of the positive electrode of the whole battery, in Ω·m; j is the imaginary unit; ω is the angular velocity; P pos is the non-ideal capacitance coefficient of the positive electrode of the full battery; C dlpos is the interfacial capacitance of the positive electrode of the whole battery, in F / m; S pos is the area of ​​the positive electrode material of the whole battery, in m 2 ξ neg is the interfacial impedance of the negative electrode of the whole battery; R ctneg is the interfacial resistance of the negative electrode of the whole battery, in Ω·m; j is the imaginary unit; ω is the angular velocity; P neg is the non-ideal capacitance coefficient of the negative electrode of the whole battery; C dlneg is the interfacial capacitance of the negative electrode of the whole battery, in F / m; S neg is the area of ​​the negative electrode material of the whole battery, in m 2 .

10. The in-situ measurement method of battery tortuosity according to claim 1, characterized in that: The method for optimizing the electrochemical impedance spectroscopy includes one or more of a heuristic algorithm, a least squares method or a conjugate gradient method.

Images