Lithium battery state estimation stress parameter identification method and related equipment

Abstract

The invention provides a lithium battery state estimation stress parameter identification method and related equipment, and relates to the technical field of lithium battery state analysis. The method comprises the following steps: implementing a lithium battery charging test, and respectively acquiring an operation voltage and a mechanical pressure under stress-free and stress working conditions; lithium battery state values are calculated and comprise a plurality of parameters such as average stress, operation current and negative electrode potential, and state information is provided for subsequent stress parameter identification; and constructing a stress-induced reaction area degradation equation, and identifying stress parameters of reaction area index type degradation in combination with voltage and pressure test data. From the perspective of the electrode reaction area, the internal mechanism that the mechanical stress affects the electrochemical reaction of the lithium battery is disclosed, the stress-induced reaction area recession model is constructed, the efficient, simple and convenient stress parameter identification method is provided, and the lithium battery state estimation precision can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery state analysis, and in particular to a lithium battery state estimation stress parameter identification method and related equipment. Background Art

[0002] Lithium batteries are widely used in electric vehicles, portable devices, energy storage systems and other fields due to their high energy density, long cycle life and low self-discharge rate. Lithium battery state estimation is an important tool to ensure its service performance, involving the coupled analysis of multiple physical fields such as electrochemistry, heat and mechanics. The electrochemical reaction process of lithium batteries includes not only the positive reaction of lithium extraction / insertion, but also a series of complex side reactions, such as solid electrolyte interface decomposition and electrolyte decomposition. Most of these reactions involve the reaction area of ​​the negative electrode particles. Existing studies usually convert the reaction area from a macroscopic perspective into the specific surface area from a microscopic perspective, by treating the negative electrode particles as spheres and using geometric equations (taking into account factors such as porosity and particle radius) to calculate the reaction area per unit volume. This method is applicable to ideal working conditions, but does not consider the influence of mechanical stress on the specific surface area, resulting in insufficient accuracy in lithium battery state estimation.

[0003] Theoretical and experimental studies have shown that mechanical stress exists inside lithium battery electrodes under assembly conditions, which has a significant impact on the specific surface area of ​​the electrochemical reaction, leading to the degradation of lithium battery performance. Taking the lithium insertion reaction during the charging process as an example, the negative electrode carbon particles expand during lithium insertion, and the spatial constraints under assembly conditions induce mechanical stress, which in turn leads to the compaction of the negative electrode pores and the deterioration of particle contact, forming a "dead zone" effect, reducing the effective area for lithium insertion reaction. Mechanical stress also introduces additional voltage drop, resulting in an increase in the voltage of side reactions, which in turn accelerates the growth of the solid electrolyte interface, consumes active lithium, and ultimately accelerates the degradation of battery capacity.

[0004] Existing research on lithium battery state estimation and early warning has taken into account the influence of mechanical stress. For example, CN202510637487.2 discloses a battery thermal runaway early warning system and method, which uses the stress information obtained by the sensor as an early warning criterion. CN202510622556.2 provides a high-precision SOC monitoring method for lithium iron phosphate energy storage power stations based on Kalman filtering, and iteratively updates the stress-capacity decay correlation model using a machine learning method. CN202510417927.3 discloses a method and system for in-situ measurement of hard-shell lithium battery strain, which solves the problem of measuring stress and strain of hard-shell lithium batteries. CN202510399687.9 discloses a battery state of charge estimation system based on mechanical-electrochemical fusion, which corrects the state of charge estimation result through stress sensing signals. CN202510376348.9 discloses a method for estimating the cycle stress and stress reliability of silicon-carbon lithium batteries, which can efficiently calculate the probability of peak stress exceeding the limit under cyclic conditions. CN202510358630.4 discloses a sulfonyl-containing high-voltage positive electrode adhesive and a preparation method, as well as a battery positive electrode and a lithium-ion battery, which are intended to buffer the stress generated by volume changes during long-term charging and discharging. CN202510351604.9 discloses an electrode interface modification material, an electrode and a lithium-ion battery, which can effectively release the stress changes caused by the volume changes of the electrode during charging and discharging. Analysis of the patent results shows that mechanical stress has a significant impact on the service performance of lithium batteries, which has become an industry consensus; researchers try to monitor the battery status by collecting stress information, or develop lithium battery materials or structures to reduce mechanical stress. Research on the physical model of lithium batteries that constructs stress to affect electrochemistry and clarifies the stress parameter identification mechanism is urgently needed.

[0005] To this end, from the perspective of electrode reaction area, the intrinsic mechanism of how mechanical stress affects the electrochemical reaction of lithium batteries is revealed, a stress-induced reaction area decay model is constructed, and an efficient and simple stress parameter identification method is proposed, which has important engineering significance for ensuring the performance and service safety of lithium batteries. Summary of the Invention

[0006] This invention overcomes the shortcomings of existing technologies and provides a method and related equipment for stress parameter identification for lithium battery state estimation. First, a lithium battery charging test is conducted to obtain the operating voltage and mechanical pressure under both stress-free and stress-exposed conditions. Second, the lithium battery state values ​​are calculated, including multiple parameters such as average stress, operating current, and cathode potential, providing state information for subsequent stress parameter identification. Finally, a stress-induced reaction area degradation equation is constructed and, combined with voltage and pressure test data, the stress parameters for exponential degradation of the reaction area are identified.

[0007] To achieve the above objectives, an embodiment of the present invention provides a method for identifying stress parameters for lithium battery state estimation, the method comprising the following processing steps:

[0008] Step S1: Implement a lithium battery charging test.

[0009] Step S2: Calculate the lithium battery status value.

[0010] Step S3: Identify state estimation stress parameters.

[0011] Furthermore, in step S1, the lithium battery charging test has the following characteristics: the experimental object is a prismatic lithium battery, and two test conditions are used: a stress-free condition and a stress-free condition. The stress-free condition refers to suspending the lithium battery in a zero-charge state and charging the lithium battery 20 at a constant current rate of 0.5C using a battery performance tester at an ambient temperature of 25°C; 0.5C indicates that the operating current is 0.5 times the nominal charge capacity of the battery. The stress-free condition refers to placing the lithium battery in a zero-charge state between an upper metal plate and a lower metal plate, with a planar pressure sensor installed between the lithium battery and the lower metal plate, and a fixed height between the upper metal plate 21 and the lower metal plate 22 forming a fixed spatial constraint for the lithium battery; the lithium battery is charged at a constant current rate of 0.5C using a battery performance tester at an ambient temperature of 25°C. The average operating voltages under the two conditions are collected and written as U0 and U; U0 represents the average operating voltage for stress-free charging, and U represents the average operating voltage for stress-free charging. For the stress condition, the average surface pressure is collected by a plane pressure sensor and written as FM, where FM represents the average pressure during the charging process.

[0012] Furthermore, in the step S2, the calculation of the lithium battery status value includes the following steps.

[0013] Step S2.1: Calculate the average stress, which is expressed as formula (1): σ = FM / (W*L); where σ represents the average stress, W represents the width of the lithium battery, and L represents the length of the lithium battery.

[0014] Step S2.2: Calculate the operating current, written as formula (2): I = Q0*CR; where I represents the operating current, CR represents the rate, and a negative sign represents charging; Q0 represents the nominal capacity of the lithium battery.

[0015] Step S2.3: Calculate the negative electrode liquid phase volume fraction, written as formula (3): εe = 1-εs-εf; where εe represents the negative electrode liquid phase volume fraction, εs represents the negative electrode solid phase volume fraction, and εf represents the inert solid volume fraction.

[0016] Step S2.4: Calculate the total area of ​​the negative electrode, which can be expressed as formula (4): A = W*L*N; where A represents the total area of ​​the negative electrode, and N represents the number of negative electrode layers.

[0017] Step S2.5: Calculate the negative electrode solid phase potential, which can be expressed as formula (5): φs = I*δ / (2*A*KC*εs^b); where φs represents the negative electrode solid phase potential, δ represents the negative electrode thickness, KC represents the negative electrode solid phase effective conductivity, and b represents the Bruggeman porosity index, which is usually 1.5.

[0018] Step S2.6: Calculate the negative electrode liquid phase potential, written as formula (6): φe = -I*δ / (2*A*KE*εe^b); where φe represents the negative electrode liquid phase potential and KE represents the effective conductivity of the electrolyte.

[0019] Step S2.7: Calculate the initial value of the reaction specific surface area, written as formula (7): An0 = 3*εs / r; where An0 represents the initial value of the reaction specific surface area, and r represents the radius of the negative electrode solid phase particle.

[0020] Step S2.8: Calculate the lithium insertion reaction current volume density, expressed as formula (8): Jn = I / (A*δ); where Jn represents the lithium insertion reaction current volume density. Formula (8) is derived from the definition of current volume density, i.e., the operating current per unit volume of the negative electrode.

[0021] Step S2.9: Calculate the overpotential under stress-free conditions, expressed as formula (9): η0 = φs - φe.

[0022] Furthermore, in the step S3, the identification state estimation stress parameter includes the following steps.

[0023] Step S3.1: Calculate the overpotential under stress conditions, which can be expressed as formula (10): η = η0 + U0 - U, where η represents the overpotential under stress conditions.

[0024] Step S3.2: Calculate the solid-liquid potential difference under stress conditions, expressed as formula (11): Δφ=φs﹣φe﹣VL*σ / F; Δφ represents the solid-liquid potential difference under stress conditions; VL represents the partial molar volume of lithium ions, which is a constant of 1300 mm^3 / mol; F represents the Faraday constant, i.e., 96485 C / mol.

[0025] Step S3.3: Calculate the effective value of the specific reaction area, which is expressed as formula (12): An = Jn*GS / (η-Δφ); where An represents the effective value of the specific reaction area, and GS represents the SEI impedance.

[0026] Step S3.4: Calculate the stress parameter, which is expressed as formula (13): β = -ln(An / An0) / σ; where β represents the stress parameter, i.e., the stress-induced reaction area degradation index.

[0027] An embodiment of the present invention further provides a device for identifying stress parameters of a lithium battery state estimation, the device comprising:

[0028] Test module, used to implement lithium battery charging test;

[0029] Calculation module, used to calculate the lithium battery status value;

[0030] Identification module, used to identify state estimation stress parameters.

[0031] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the above-mentioned method for identifying stress parameters for estimating the state of a lithium battery are implemented.

[0032] An embodiment of the present invention also provides an electronic device, including a processor and a memory, which are interconnected, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute the steps of the above-mentioned lithium battery state estimation stress parameter identification method.

[0033] Compared with the existing technology, the stress parameter identification method for lithium battery state estimation proposed in the present invention has the following advantages: In terms of innovation, it proposes a stress-induced reaction area degradation equation, revealing that the specific area of ​​the lithium insertion reaction degrades exponentially with increasing stress; compared with traditional state estimation models that treat the specific surface area of ​​the lithium insertion reaction as a constant value independent of stress, this degradation equation describes the effect of mechanical stress on the lithium insertion reaction. Introducing this degradation equation can improve the accuracy of related lithium battery state estimation models. In terms of applicability, the method of the present invention establishes conventional charging test conditions, obtains operating voltage and mechanical pressure, and indirectly calculates the stress parameters for lithium battery state estimation, thereby solving the problem of stress parameter identification in lithium battery state estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flow chart of a stress parameter identification method for estimating lithium battery state according to a specific application example of the present invention is shown.

[0035] Figure 2 The figure shows a structural diagram of a stress parameter identification device for estimating the state of a lithium battery according to a specific application example of the present invention.

[0036] Reference numerals: 20, lithium battery; 21, upper metal plate; 22, lower metal plate; 23, planar pressure sensor. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with an embodiment, but this does not constitute any limitation to the present invention. Any limited number of modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0038] The present invention provides a method for identifying stress parameters of lithium battery state estimation, such as Figure 1 As shown, the method includes the following steps.

[0039] Step S1: Implement a lithium battery charging test.

[0040] Step S2: Calculate the lithium battery status value.

[0041] Step S3: Identify the state and estimate the stress parameters. Step S1: Implement a lithium battery charging test. In an embodiment of the present invention, the method can be applied to a square lithium battery 20 to illustrate the processing steps and method performance. The positive and negative electrode materials of the lithium battery 20 are lithium cobalt oxide and graphite, respectively, and the main components of the electrolyte are lithium hexafluorophosphate and carbonate solvents. The lithium battery charging test conditions include: stress-free conditions and stress conditions. The stress-free condition refers to suspending a lithium battery in a zero-charge state, and using a battery performance tester to perform a 0.5C constant current charge on the lithium battery 20 at an ambient temperature of 25°C; 0.5C means that the operating current is 0.5 times the nominal charge capacity of the battery. As Figure 2 As shown, the stressed operating condition involves placing a zero-charge lithium battery 20 between an upper metal plate 21 and a lower metal plate 22. A planar pressure sensor 23 is positioned between the lithium battery 20 and the lower metal plate 22. The fixed height between the upper and lower metal plates 21, 22 creates a fixed spatial constraint 24 for the lithium battery. The lithium battery is then charged at a constant current rate of 0.5C using a battery performance tester at an ambient temperature of 25°C. The average operating voltage values ​​under the two operating conditions are collected and denoted as U0 and U. U0 represents the average operating voltage value for unstressed charging, while U represents the average operating voltage value for stressed charging. For the stressed operating condition, the average surface pressure is collected using a planar pressure sensor and denoted as FM, where FM represents the average planar pressure value during the charging process. In this embodiment, the battery performance tester is model CTS-5V10A@REPOWER, and the planar pressure sensor is model DJYB-200A@DIJIA. The corresponding sampling interval for the average operating voltage and planar pressure values ​​is from 20% to 80% of the charge capacity during the charging process.

[0042] It should be noted that the charging experiment was conducted because during the charging phase, lithium ions migrate from the positive electrode through the separator to the negative electrode and embed themselves in the carbon particles there, forming lithium carbide. During this lithium embedding process, the negative electrode potential is high, which can easily induce the side reaction of SEI growth, consuming some of the active lithium. During the discharge phase, lithium ions migrate back to the positive electrode, where the negative electrode potential is lower and less likely to induce side reactions.

[0043] Step S2: Calculating the lithium battery status value, including the following steps.

[0044] Step S2.1: Calculate the mean stress, expressed as Equation (1): σ = FM / (W * L); where σ represents the mean stress, W represents the width of the lithium battery, and L represents the length of the lithium battery. Equation (1) is derived from the classic method for calculating plane pressure, where pressure is equal to the uniformly distributed pressure divided by the area under force, and the external pressure corresponds to the normal stress of the lithium battery.

[0045] Step S2.2: Calculate the operating current using Equation (2): I = Q0 * CR; where I represents the operating current, CR represents the charge rate, and a negative sign indicates charging; Q0 represents the nominal capacity of the lithium battery. Equation (2) is derived from the definition of the charge rate, i.e., 1C represents the operating current equal to 1 times the nominal charge capacity of the battery.

[0046] Step S2.3: Calculate the negative electrode liquid phase volume fraction, expressed as Equation (3): εe = 1 - εs - εf; where εe represents the negative electrode liquid phase volume fraction, εs represents the negative electrode solid phase volume fraction, and εf represents the inert solid volume fraction. Equation (3) is derived from the assumption that the sum of the negative electrode component proportions is 1, and the negative electrode includes a solid phase, a liquid phase, and an inert solid. In this embodiment, the negative electrode solid phase is graphite particles, the negative electrode liquid phase is the electrolyte, and the inert solids are inactive components such as the conductive agent and binder.

[0047] Step S2.4: Calculate the total negative electrode area using Equation (4): A = W * L * N, where A represents the total negative electrode area and N represents the number of negative electrode layers. Equation (4) derives from the fact that the total negative electrode area is equal to the area of ​​each negative electrode (i.e., length times width) multiplied by the number of electrode layers.

[0048] Step S2.5: Calculate the negative electrode solid phase potential, expressed as Equation (5): φs = I*δ / (2*A*KC*εs^b); where φs represents the negative electrode solid phase potential, δ represents the negative electrode thickness, KC represents the negative electrode solid phase effective conductivity, and b represents the Bruggeman porosity index, typically set to 1.5. Equation (5) is derived from the classic Butler-Volmer electrochemical reaction equation and describes the relationship between the negative electrode solid phase potential, current density, and solid phase material properties.

[0049] Step S2.6: Calculate the negative electrode liquid phase potential, expressed as Equation (6): φe = -I*δ / (2*A*KE*εe^b); where φe represents the negative electrode liquid phase potential and KE represents the effective conductivity of the electrolyte. Equation (6) is derived from the classic Butler-Volmer electrochemical reaction equation and describes the relationship between the negative electrode liquid phase potential, current density, and liquid phase material properties.

[0050] Step S2.7: Calculate the initial value of the reaction specific surface area, expressed as Equation (7): An0 = 3*εs / r; where An0 represents the initial value of the reaction specific surface area, and r represents the radius of the negative electrode solid phase particle. Equation (7) is derived from a classical geometric equation that describes the lithium insertion reaction area per unit volume of the negative electrode solid phase spherical particle.

[0051] Step S2.8: Calculate the lithium insertion reaction current volume density, expressed as formula (8): Jn = I / (A*δ); where Jn represents the lithium insertion reaction current volume density. Formula (8) is derived from the definition of current volume density, i.e., the operating current per unit volume of the negative electrode.

[0052] Step S2.9: Calculate the overpotential under stress-free conditions, expressed as Equation (9): η0 = φs - φe. Equation (9) is derived from the definition of the overpotential for driving the electrochemical reaction at the negative electrode, i.e., the overpotential is the solid-liquid potential difference.

[0053] Step S3: Identify state and estimate stress parameters, including the following steps.

[0054] Step S3.1: Calculate the overpotential under stress conditions, expressed as Equation (10): η = η0 + U0 - U, where η represents the overpotential under stress conditions. Equation (10) is derived from the potential balance equation η - η0 = U0 - U. The left side of this equation is the operating voltage difference between stress and no-stress conditions, that is, the operating voltage deviation caused by stress, and the right side is the overpotential correction value caused by stress and no-stress conditions. In step S1, under room temperature, 0.5C constant current and constant voltage charging conditions, the lithium battery charging is in an ideal state, and the interference of temperature fluctuations, fast charging and discharging, and overcharging and discharging on the potential can be eliminated. Therefore, only the influence of stress needs to be considered, and according to the principle of potential balance, this equation holds. In step S1, U and U0 are measured through the lithium battery charging test. Combined with Equation (9), η, which cannot be directly measured, can be indirectly obtained.

[0055] Step S3.2: Calculate the solid-liquid potential difference under stress, expressed as Equation (11): Δφ = φs - φe - VL*σ / F, where Δφ represents the solid-liquid potential difference under stress; VL represents the partial molar volume of lithium ions, which is a constant of 1300 mm³ / mol; and F represents the Faraday constant, which is 96485 C / mol. Equation (11) is derived from existing electrochemical / mechanical coupling theory. VL*σ / F is the stress correction term, which quantitatively describes how the volume change of the electrode under stress affects lithium ion insertion.

[0056] Step S3.3: Calculate the effective value of the specific reaction area, expressed as Equation (12): An = Jn*GS / (η - Δφ); where An represents the effective value of the specific reaction area and GS represents the SEI impedance. Equation (12) is derived by transforming the overpotential calculation formula η = Δφ + Jn*GS / An. Jn*GS / An is derived from classical electrical impedance theory and describes the effect of the SEI film on the negative electrode surface on the overpotential of the lithium insertion reaction.

[0057] Step S3.4: Calculate the stress parameter, expressed as Equation (13): β = -ln(An / An0) / σ; where β represents the stress parameter, i.e., the stress-induced reaction area degradation exponent. Equation (13) is derived from the stress-induced reaction area degradation equation An = An0*exp(-β*σ), which is proposed for the first time in this invention. The reasons for its construction and the proposed mathematical form are explained as follows. Existing theoretical and experimental studies show that the negative electrode is subjected to mechanical stress during cycling, resulting in the gradual compaction of its porous composite structure and the deterioration of interparticle contact, thereby forming a "dead zone" for lithium insertion reaction in local areas. Under normal operating conditions, the stress range is typically 0-1.0 MPa. For example, the pressure release threshold of prismatic lithium batteries is typically set between 0.8 MPa and 1.0 MPa. Within this stress range, increasing stress causes the effective specific surface area to exhibit a nonlinear downward trend: the rate of decrease in specific surface area gradually slows, eventually approaching a state of equilibrium. The method of the present invention characterizes the negative electrode structural degradation behavior caused by mechanical stress and proposes a stress-driven reaction specific surface area degradation mechanism; drawing on the mathematical form of the Arrhenius law in chemical reaction kinetics, the stress-induced reaction area degradation equation is constructed.

[0058] The specifications of the lithium battery 20 in this embodiment are listed in Table 1. To verify the robustness of the method of the present invention, three initial conditions were set for the stress condition in step S1: ① initial pressure 980N (10Kg); ② initial pressure 245N (25Kg); and ③ initial pressure 392N (40Kg). The pressure and voltage of the three initial conditions were averaged to form the test value of the comprehensive condition ④. The lithium battery discharge test data and calculation results under the four stress conditions are listed in Table 2. The stress parameter identification results under the four conditions converged within the range of 2.657-3.017, with a standard deviation of 0.149 and a coefficient of variation of 5.22%. It is generally believed that a coefficient of variation of ≤10% indicates low dispersion, that is, low-dispersion stress parameter results were obtained under multiple stress conditions. This shows that the stress parameter identification method proposed by the method of the present invention has high robustness and the constructed stress-induced reaction area degradation equation has good physical interpretation.

[0059] This embodiment shows that the stress parameter identification method for lithium battery state estimation provided by the method of the present invention has the following advantages. In terms of innovation, a stress-induced reaction area degradation equation is proposed, which reveals the law that the specific surface area of ​​the lithium insertion reaction degenerates exponentially with increasing stress; compared with the traditional state estimation model, the specific surface area of ​​the lithium insertion reaction is regarded as a constant value independent of stress. The degradation equation describes the influence of mechanical stress on the lithium insertion reaction. The introduction of the degradation equation can improve the accuracy of the relevant lithium battery state estimation model. In terms of applicability, the method of the present invention establishes conventional charging test conditions, obtains operating voltage and mechanical pressure, and indirectly calculates the stress parameters of the lithium battery state estimation, thereby solving the problem of stress parameter identification in lithium battery state estimation.

[0060] Table 1

[0061] parameter W L H Q0 N δ r εs εf KC KE GS unit mm mm mm Ah - mm mm - - S / mm S / mm <![CDATA[Ω·mm 2 ]]> Numerical 61.5 77.3 5.1 4.51 16 0.12 0.004 0.67 0.07 0.13 0.0012 8350

[0062] Table 2

[0063]

Claims

1. A method for identifying stress parameters for lithium battery state estimation, characterized in that: The method comprises the following processing steps: Step S1: Implementing a lithium battery charging test; Step S2: Calculate the lithium battery status value; Step S3: Identify state estimation stress parameters.

2. The method according to claim 1, characterized in that In step S1, the experimental object of the lithium battery charging test is a square lithium battery, and the two test conditions are a stress-free condition and a stress condition; the stress-free condition refers to suspending the lithium battery in a zero-charge state and using a battery performance tester to perform 0.5C constant-current charging on the lithium battery at an ambient temperature of 25°C; 0.5C means that the operating current is 0.5 times the nominal charge capacity of the battery; the stress condition refers to placing the lithium battery in a zero-charge state between an upper metal plate and a lower metal plate, and a planar pressure sensor is provided between the lithium battery and the lower metal plate, and the fixed height between the upper metal plate and the lower metal plate forms a fixed spatial constraint on the lithium battery; the lithium battery is charged at a 0.5C constant-current rate using a battery performance tester at an ambient temperature of 25°C; the average operating voltages under the two conditions are collected and written as U0 and U; U0 represents the average operating voltage of the stress-free charging operation; U represents the average operating voltage of the stress-charged operation; for the stress condition, the average surface pressure is collected by the planar pressure sensor and written as FM, where FM represents the average pressure during the charging process.

3. The method according to claim 1, characterized in that In the step S2, the calculation of the lithium battery status value includes the following steps: Step S2.1: Calculate the average stress, expressed as formula (1): σ = FM / (W * L); where σ represents the average stress, W represents the width of the lithium battery, and L represents the length of the lithium battery; Step S2.2: Calculate the operating current, expressed as formula (2): I = Q0 * CR; Where I represents the operating current, CR represents the rate, and a negative sign represents charging; Q0 represents the nominal capacity of the lithium battery; Step S2.3: Calculate the negative electrode liquid phase volume fraction, written as formula (3): εe = 1-εs-εf; where εe represents the negative electrode liquid phase volume fraction, εs represents the negative electrode solid phase volume fraction; εf represents the inert solid volume fraction; Step S2.4: Calculate the total area of ​​the negative electrode, written as formula (4): A = W*L*N; where A represents the total area of ​​the negative electrode, and N represents the number of negative electrode layers; Step S2.5: Calculate the negative electrode solid phase potential, written as formula (5): in, represents the negative electrode solid phase potential, δ represents the negative electrode thickness; KC represents the negative electrode solid phase effective conductivity; b represents the Bruggeman porosity index, which is usually taken as 1.5; Step S2.6: Calculate the negative electrode liquid phase potential, written as formula (6): in, represents the negative electrode liquid phase potential, KE represents the effective conductivity of the electrolyte; Step S2.7: Calculate the initial value of the reaction specific surface area, expressed as formula (7): An0 = 3*εs / r; where An0 represents the initial value of the reaction specific surface area, and r represents the radius of the negative electrode solid phase particle; Step S2.8: Calculate the lithium insertion reaction current volume density, expressed as formula (8): Jn = I / (A*δ); where Jn represents the lithium insertion reaction current volume density; Formula (8) is derived from the definition of current volume density, i.e., the operating current per unit volume of the negative electrode; Step S2.9: Calculate the overpotential under stress-free conditions, expressed as Equation (9):

4. The method according to claim 1, wherein In the step S3, the identification state estimates stress parameters, The following steps are included: Step S3.1: Calculate the overpotential under stress conditions, expressed as formula (10): η = η0 + U0 - U, where η represents the overpotential under stress conditions; Step S3.2: Calculate the solid-liquid potential difference under stress conditions, expressed as formula (11): Δφ=φs﹣φe﹣VL*σ / F; Δφ represents the solid-liquid potential difference under stress conditions; VL represents the partial molar volume of lithium ions, which is a constant of 1300 mm^3 / mol; F represents the Faraday constant, which is 96485 C / mol; Step S3.3: Calculate the effective value of the reaction specific area, expressed as formula (12): An = Jn*GS / (η-Δφ); Where An represents the effective value of the reaction specific area, and GS represents the SEI impedance; Step S3.4: Calculate the stress parameter, which is expressed as formula (13): β = -ln(An / An0) / σ; where β represents the stress parameter, i.e., the stress-induced reaction area degradation index.

5. A lithium battery state estimation stress parameter identification device, characterized in that: The device comprises: Test module, used to implement lithium battery charging test; Calculation module, used to calculate the lithium battery status value; Identification module, used to identify state estimation stress parameters.

6. The device according to claim 5, characterized in that The experimental object of the lithium battery charging test is a square lithium battery, and the two test conditions are stress-free condition and stress-exposed condition. The stress-free condition refers to suspending the lithium battery in a zero-charge state and charging the lithium battery at a constant current rate of 0.5C using a battery performance tester at an ambient temperature of 25°C. 0.5C means that the operating current is 0.5 times the nominal charge capacity of the battery. The stress condition refers to placing the lithium battery in a zero-charge state between an upper metal plate and a lower metal plate, and a planar pressure sensor is provided between the lithium battery and the lower metal plate. The fixed height between the upper metal plate and the lower metal plate forms a fixed spatial constraint on the lithium battery. The lithium battery is charged at a constant current rate of 0.5C using a battery performance tester at an ambient temperature of 25°C. The average operating voltages under the two conditions are collected and written as U0 and U. U0 represents the average operating voltage of the stress-free charging operation; U represents the average operating voltage of the stress-exposed charging operation. For the stress condition, the average surface pressure is collected by the planar pressure sensor and written as FM, where FM represents the average pressure during the charging process.

7. The device according to claim 5, characterized in that The calculation module is specifically used for: Calculate the average stress and write it as formula (1): σ = FM / (W*L); where σ represents the average stress, W represents the width of the lithium battery, and L represents the length of the lithium battery; Calculate the operating current and write it as formula (2): I = Q0*CR; Where I represents the operating current, CR represents the rate, and a negative sign represents charging; Q0 represents the nominal capacity of the lithium battery; Calculate the negative electrode liquid phase volume fraction, written as formula (3): εe = 1-εs-εf; where εe represents the negative electrode liquid phase volume fraction, εs represents the negative electrode solid phase volume fraction; εf represents the inert solid volume fraction; Calculate the total area of ​​the negative electrode and write it as formula (4): A = W*L*N; where A represents the total area of ​​the negative electrode and N represents the number of negative electrode layers; Calculate the negative electrode solid phase potential and write it as formula (5): in, represents the negative electrode solid phase potential, δ represents the negative electrode thickness; KC represents the negative electrode solid phase effective conductivity; b represents the Bruggeman porosity index, which is usually taken as 1.5; Calculate the negative electrode liquid phase potential and write it as formula (6): in, represents the negative electrode liquid phase potential, KE represents the effective conductivity of the electrolyte; Calculate the initial value of the reaction specific surface area and write it as formula (7): An0 = 3*εs / r; where An0 represents the initial value of the reaction specific surface area and r represents the radius of the negative electrode solid phase particle; The lithium insertion reaction current volume density is calculated as follows: Jn = I / (A*δ); where Jn represents the lithium insertion reaction current volume density; Formula (8) is derived from the definition of current volume density, i.e., the operating current per unit volume of the negative electrode; Calculate the overpotential under stress-free conditions and write it as formula (9):

8. The device according to claim 5, characterized in that The identification module is specifically used for: The overpotential under stress conditions is calculated as follows: η = η0 + U0 - U, where η represents the overpotential under stress conditions; The solid-liquid potential difference under stress conditions is calculated as follows: Δφ=φs﹣φe﹣VL*σ / F; Δφ represents the solid-liquid potential difference under stress conditions; VL represents the partial molar volume of lithium ions, which is a constant of 1300 mm^3 / mol; F represents the Faraday constant, which is 96485 C / mol; Calculate the effective value of the reaction specific area and write it as formula (12): An=Jn*GS / (η﹣Δφ); Where An represents the effective value of the reaction specific area, and GS represents the SEI impedance; The stress parameter is calculated as formula (13): β = -ln(An / An0) / σ; where β represents the stress parameter, that is, the stress-induced reaction area degradation index.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the lithium battery state estimation stress parameter identification method according to any one of claims 1 to 4.

10. An electronic device, characterized in that: The invention comprises a processor and a memory, wherein the processor and the memory are connected to each other, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute the steps of the lithium battery state estimation stress parameter identification method according to any one of claims 1 to 4.

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