Method for estimating lithium ion concentration on the surface of lithium battery under non-disassembly condition

Abstract

The present application relates to the technical field of lithium battery testing, and particularly relates to a method for estimating the solid-phase surface lithium ion concentration of a lithium battery without disassembly, which mainly solves the technical problem that existing methods for estimating the solid-phase surface lithium ion concentration cannot take into account the integrity of the lithium battery, the simplicity of the model and the physical interpretability. The method comprises obtaining constant-current charge-discharge data of the lithium battery at multiple rates and calculating the state of charge of the battery; selecting the lowest rate to construct a reference open-circuit voltage curve; establishing a linear mapping relationship between the state of charge of the battery and the average lithium intercalation degree of the positive and negative electrodes based on the equilibrium potential curves of the positive and negative electrode materials; constructing a polarization model composed of the concentration polarization voltage and the residual polarization voltage and identifying the model parameters to obtain a surface lithium intercalation degree estimation model; and outputting the surface lithium intercalation degree of the positive and negative electrodes and calculating the solid-phase surface lithium ion concentration in combination with the maximum solid-phase lithium ion concentration. The method can accurately estimate the solid-phase surface lithium ion concentration without disassembling the battery and has physical interpretability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery testing technology, and in particular to a method for estimating the lithium ion concentration on the solid surface of a lithium battery without disassembly. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage power stations, and portable electronic devices, lithium batteries have been widely used due to their advantages such as high energy density, long cycle life, and high charge-discharge efficiency. In the electrochemical reaction process of lithium batteries, the lithium-ion concentration on the solid surface of the positive and negative electrodes is a crucial variable determining the insertion / extraction reaction, electrode equilibrium potential, and concentration polarization. Accurately obtaining the lithium-ion concentration on the solid surface of the positive and negative electrodes is of great significance for state estimation, fault warning, lifespan prediction, and safety control of battery management systems.

[0003] Since the lithium-ion concentration on the solid surface of the positive and negative electrodes is difficult to measure directly through external battery testing, existing technologies typically employ disassembly testing or model analysis to obtain information about the battery's internal state. Disassembly testing can directly obtain internal reaction characteristics such as electrode material state and electrode morphology changes, but this method damages the battery structure, is complex, and is difficult to use for online detection and engineering applications. Model analysis methods mainly include electrochemical mechanism modeling and data-driven methods. Electrochemical mechanism modeling can describe the battery's internal state from the perspective of reaction kinetics and mass transfer processes, and can solve for the solid-phase lithium-ion concentration distribution, but it often requires a large number of physical parameters that are difficult to measure directly, and the model calculations are complex and parameter identification is difficult. Data-driven methods can establish a mapping relationship between battery state and external measurement signals using a large amount of charge and discharge data, but relying solely on external data such as terminal voltage, current, and capacity for black-box fitting makes it difficult to guarantee that the estimation results have a clear physical meaning.

[0004] Therefore, there is an urgent need for a method for estimating the lithium-ion concentration on a solid surface that does not require disassembling the battery, is easy to calculate using a model, and whose estimation results have clear physical meaning. Summary of the Invention

[0005] To overcome the technical shortcomings of existing methods for estimating lithium-ion concentration on solid-phase surfaces, which cannot simultaneously consider the integrity of lithium batteries, model simplicity, and physical interpretability, this invention proposes a method for estimating lithium-ion concentration on solid-phase surfaces of lithium batteries without disassembly.

[0006] The method for estimating lithium-ion concentration on the solid surface of a lithium battery without disassembly provided by this invention includes the following steps:

[0007] S1. Obtain constant current charge and discharge data of lithium battery at multiple rates, wherein the constant current charge and discharge data includes time data, voltage data, current data and capacity data, and obtain the rated capacity of lithium battery;

[0008] S2. Based on the capacity data and the rated capacity, calculate the battery state of charge at each rate to obtain the corresponding curve of battery state of charge (SOC) and voltage at each rate;

[0009] S3. Select the lowest rate among multiple rates, obtain the charging voltage curve and the discharging voltage curve from the constant current charging and discharging data of the lowest rate, and construct a reference open circuit voltage (reference OCV) curve based on the average value of the charging voltage curve and the discharging voltage curve. The reference open circuit voltage curve is used to characterize the relationship between the voltage of the lithium battery in equilibrium state and the state of charge of the battery.

[0010] S4. Obtain the equilibrium potential curves of the positive and negative electrode materials, and establish a linear mapping relationship between the battery state of charge and the average degree of lithium intercalation based on the equilibrium potential curves, and calculate the reconstructed open circuit voltage (reconstructed OCV); based on the reference open circuit voltage curve, identify the linear mapping parameters between the battery state of charge and the average degree of lithium intercalation.

[0011] S5. Based on the electrochemical characteristics of lithium batteries under constant current conditions, a concentration polarization voltage caused by lithium intercalation deviation is introduced on the basis of the reconstructed open circuit voltage, and together with the remaining polarization voltage, a polarization model is formed. The reconstructed terminal voltage is calculated based on the polarization model.

[0012] S6. Based on constant current charge and discharge data at multiple rates, identify the model parameters of the polarization model, including the equivalent coefficient of positive and negative electrode lithium intercalation deviation and the residual polarization voltage at each rate, to obtain the surface lithium intercalation estimation model.

[0013] S7. Obtain the maximum solid-phase lithium-ion concentration of the positive and negative electrode materials, and output the surface lithium intercalation degree of the positive and negative electrodes through the surface lithium intercalation degree estimation model; calculate the solid-phase surface lithium-ion concentration based on the maximum solid-phase lithium-ion concentration and the surface lithium intercalation degree of the positive and negative electrodes.

[0014] Further, in step S2, the battery state of charge is calculated using the following formula:

[0015] ;

[0016] in, Indicates the battery state of charge at a given time. Indicates the initial state of battery charge. This indicates the cumulative charging and discharging capacity at any given time. This indicates the actual total usable capacity of the battery under the current operating conditions.

[0017] Further, in step S3, the expression for the reference open-circuit voltage curve is:

[0018] ;

[0019] in, Indicates the reference open-circuit voltage. The constant current charging voltage curve represents the lowest charging rate. The constant current discharge voltage curve represents the lowest discharge rate.

[0020] Further, in step S4, the reconstructed open-circuit voltage is calculated using the following formula:

[0021] ;

[0022] in, This indicates the average degree of lithium intercalation in the positive electrode. This indicates the average degree of lithium intercalation in the negative electrode. The boundary value of the positive electrode lithium intercalation degree is represented at that time. The boundary value of the positive electrode lithium intercalation degree is represented at that time. The boundary value of the negative electrode lithium intercalation degree is represented at that time. The boundary value of the negative electrode lithium intercalation degree is represented at that time. Indicates the reconfigured open-circuit voltage. This represents the positive electrode equilibrium potential function. This represents the negative electrode equilibrium potential function.

[0023] Furthermore, a hybrid optimization algorithm combining differential evolution and local optimization is used to identify the linear mapping parameters between the battery's state of charge and average lithium intercalation degree. The objective function used for identification is expressed as follows:

[0024] ;

[0025] in, express Total number of sampling points This means solving a problem with the objective function as the minimum value. .

[0026] Further, in step S5, the expression for the polarization model is:

[0027] ;

[0028] in, This indicates the degree of lithium intercalation on the positive electrode surface. Indicates the degree of lithium intercalation on the negative electrode surface. This represents the equivalent coefficient for the deviation in lithium intercalation degree of the positive electrode. This represents the equivalent coefficient for the deviation of lithium intercalation degree in the negative electrode. This indicates the current under the current constant current condition. Indicates the reconfiguration terminal voltage. This represents the residual polarization voltage at the i-th multiplier.

[0029] Further, in step S6, the particle swarm optimization algorithm is used to identify the parameters of the polarization model, and the expression of the fitness function used for identification is:

[0030] ;

[0031] in, This represents the fitness function, and the total number of multipliers. This represents the measured terminal voltage.

[0032] Further, in step S7, the lithium ion concentration on the solid surface is calculated using the following formula:

[0033] ;

[0034] in, This indicates the lithium-ion concentration on the solid phase surface of the positive electrode. This indicates the lithium-ion concentration on the surface of the negative electrode solid phase. This indicates the maximum solid-phase lithium-ion concentration at the positive electrode. This indicates the maximum solid-phase lithium-ion concentration at the negative electrode.

[0035] The method for estimating lithium-ion concentration on the solid surface of a lithium battery without disassembly provided by this invention has the following advantages compared with the prior art.

[0036] 1) No battery disassembly required: This method can estimate the lithium-ion concentration on the solid surface using only externally measurable data (time, voltage, current, capacity) of the lithium battery at multiple charge and discharge rates, avoiding the damage to the battery structure caused by traditional disassembly testing. It is suitable for online testing and engineering application scenarios.

[0037] 2) Simple model calculation and few parameters: This method establishes a linear mapping relationship between SOC and average lithium intercalation degree, and a polarization model based on lithium intercalation degree deviation to characterize the surface lithium intercalation degree. The parameters that need to be identified are only the equivalent coefficients of the positive and negative electrode lithium intercalation degree deviation and the residual polarization voltage at each rate. The number of parameters is far less than the large number of physical parameters in the traditional electrochemical mechanism model, and the calculation complexity is significantly reduced.

[0038] 3) The estimation results have clear physical meaning: Each step of this method is based on the electrochemical reaction mechanism of lithium batteries. The SOC calculation is based on the physical relationship between capacity and rated capacity. The reference open-circuit voltage curve is constructed through the lowest rate charge-discharge curve to characterize the voltage characteristics of the battery in equilibrium state. The open-circuit voltage reconstruction is based on the linear mapping between the positive and negative electrode equilibrium potential curves and the degree of lithium intercalation, which has a clear electrochemical correspondence. In the polarization model, the concentration polarization voltage and the residual polarization voltage correspond to the polarization effects from different physical sources. Finally, the surface degree of lithium intercalation is converted into the solid surface lithium ion concentration through the maximum solid phase lithium ion concentration of the positive and negative electrodes. The output results can be directly used for the physical interpretation and analysis of the internal state of the battery, which is different from the pure black-box fitting of data-driven methods. Attached Figure Description

[0039] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A flowchart illustrating the overall estimation method of this invention;

[0042] Figure 2 This diagram shows the SOC-voltage curves at various rates in step S2 of the present invention.

[0043] Figure 3 This is a comparison curve between the reconstructed OCV and the reference OCV in step S4 of the present invention.

[0044] Figure 4 This represents the parameter identification result diagram in step S6 of the present invention; wherein, Figure 4 (a) shows the parameter identification results for 0.1C charging. Figure 4 (b) shows the parameter identification results for 0.1C rate discharge. Figure 4 (c) shows the parameter identification results for 2.0C charging. Figure 4 (d) shows the parameter identification results for 2.0C rate discharge;

[0045] Figure 5 This diagram illustrates the estimation results of lithium ion concentration on the solid surface in step S7 of the present invention; wherein, Figure 5 (a) shows a schematic diagram of the estimated lithium-ion concentration on the positive electrode solid surface during charging. Figure 5(b) shows a schematic diagram illustrating the estimated lithium-ion concentration on the positive electrode solid surface during discharge. Figure 5 (c) shows a schematic diagram of the estimated lithium-ion concentration on the surface of the negative electrode solid phase during charging. Figure 5 (d) shows a schematic diagram of the estimated lithium-ion concentration on the surface of the negative electrode solid phase during discharge. Detailed Implementation

[0046] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0047] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0048] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0049] Reference Figure 1 This embodiment provides a method for estimating the lithium-ion concentration on the solid surface of a lithium battery without disassembly, including steps S1 to S7.

[0050] S1. Obtain constant current charge and discharge data of the lithium battery at multiple rates, wherein the constant current charge and discharge data includes time data, voltage data, current data and capacity data, and obtain the rated capacity of the lithium battery.

[0051] Specifically, the lithium battery underwent multi-rate constant current charge-discharge testing at room temperature. Charging and discharging tests were performed separately at each rate, and time, voltage, current, and capacity data were recorded during the testing process. The lithium battery did not require disassembly during the charge-discharge tests; all data was obtained through external battery testing.

[0052] S2. Based on the capacity data and the rated capacity, calculate the battery state of charge at each rate to obtain the corresponding curve of battery state of charge versus voltage at each rate.

[0053] Specifically, the battery state of charge is calculated using the following formula:

[0054] ;

[0055] in, Indicates the battery state of charge at a given time. Indicates the initial state of battery charge. This indicates the cumulative charging and discharging capacity at any given time. This indicates the actual total usable capacity of the battery under the current operating conditions.

[0056] It is easy to understand that both SOC and voltage are time-dependent. By standardizing the time reference, the relationship between SOC and voltage can be obtained.

[0057] like Figure 2 As shown, this embodiment selects 21 voltage levels (0.05C, 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, 1.0C, 1.1C, 1.2C, 1.3C, 1.4C, 1.5C, 1.6C, 1.7C, 1.8C, 1.9C, and 2.0C) for testing. Based on the SOC and corresponding voltage data at each time point under each voltage level, SOC-voltage curves are plotted for each voltage level.

[0058] S3. Select the lowest rate among multiple rates, obtain the charging voltage curve and discharging voltage curve from the constant current charging and discharging data of the lowest rate, and construct a reference open circuit voltage curve based on the average value of the charging voltage curve and the discharging voltage curve. The reference open circuit voltage curve is used to characterize the relationship between the voltage of the lithium battery in equilibrium state and the state of charge of the battery.

[0059] Specifically, the expression for the reference open-circuit voltage curve is as follows:

[0060] ;

[0061] in, Indicates the reference open-circuit voltage. The constant current charging voltage curve represents the lowest charging rate. The constant current discharge voltage curve represents the lowest discharge rate.

[0062] It should be noted that, since the actual battery open-circuit voltage curve is difficult to obtain, this method obtains the reference open-circuit voltage based on the lowest rate operating condition, which is used as the battery open-circuit voltage.

[0063] Specifically, in this embodiment, a 0.05C rate is selected, and the charging voltage curve and discharging voltage curve at this rate are obtained. The charging voltage curve and discharging voltage curve are interpolated onto the same battery state of charge grid. The average value of the interpolated charging voltage curve and discharging voltage curve is taken according to the aforementioned formula to construct a reference open-circuit voltage curve.

[0064] S4. Obtain the equilibrium potential curves of the positive and negative electrode materials, and establish a linear mapping relationship between the battery state of charge and the average degree of lithium intercalation based on the equilibrium potential curves, and calculate the reconstructed open-circuit voltage; based on the reference open-circuit voltage curve, identify the linear mapping parameters between the battery state of charge and the average degree of lithium intercalation.

[0065] It is easy to understand that the equilibrium potential curve can be obtained from literature data, which shows the relationship between the equilibrium potential of the electrode material and the degree of lithium intercalation.

[0066] Specifically, the reconstructed open-circuit voltage is calculated using the following formula:

[0067] ;

[0068] in, This indicates the average degree of lithium intercalation in the positive electrode. This indicates the average degree of lithium intercalation in the negative electrode. The boundary value of the positive electrode lithium intercalation degree is represented at that time. The boundary value of the positive electrode lithium intercalation degree is represented at that time. The boundary value of the negative electrode lithium intercalation degree is represented at that time. The boundary value of the negative electrode lithium intercalation degree is represented at that time. Indicates the reconfigured open-circuit voltage. This represents the positive electrode equilibrium potential function. This represents the negative electrode equilibrium potential function.

[0069] It should be noted that the above formula is based on the resting thermodynamic equilibrium assumption and the simplification of the single-particle model to establish the correspondence between the reconstructed open-circuit voltage and the average degree of lithium intercalation of the positive and negative electrodes; by eliminating the influence of SEI film overpotential, electrolyte ohmic overpotential and charge transfer activation overpotential, the battery terminal voltage is decoupled to the difference between the intrinsic equilibrium potentials of the positive and negative electrode materials; the average degree of lithium intercalation of the positive and negative electrodes is represented by a linear function of the battery state of charge and four lithium intercalation boundary values, thus transforming the high-dimensional electrochemical problem into a low-dimensional parameter solution problem.

[0070] Specifically, a hybrid optimization algorithm combining differential evolution and local optimization is used to identify the linear mapping parameters between the battery's state of charge and average lithium intercalation degree, and the objective function used for identification is expressed as follows:

[0071] ;

[0072] in, express Total number of sampling points This means solving a problem with the objective function as the minimum value. .

[0073] It should be noted that the above formula uses the root mean square error of the difference between the reference open-circuit voltage and the reconstructed open-circuit voltage as the target value, and the linear mapping parameter that minimizes this target value is taken as the optimal parameter. In operation, firstly, a differential evolution algorithm is used to search for candidate parameter groups within the preset parameter boundary range to obtain a global candidate solution with a smaller target value; then, the global candidate solution is used as the initial value for local optimization, and the Powell algorithm is used to refine the candidate parameters, finally obtaining the optimal parameter, which characterizes the linear mapping relationship between the battery's state of charge and the average lithium intercalation degree of the positive and negative electrodes.

[0074] like Figure 3 As shown, this embodiment uses the aforementioned method to select the minimum root mean square error. The optimal parameters at this point are , , , As can be seen from the curve, based on this optimal parameter, the reconstructed OCV curve is in high agreement with the reference OCV, proving the accuracy of the linear mapping relationship in reconstructing the battery open-circuit voltage.

[0075] S5. Based on the electrochemical characteristics of lithium batteries under constant current conditions, the concentration polarization voltage caused by the lithium intercalation degree deviation is introduced on the basis of the reconstructed open circuit voltage, and together with the remaining polarization voltage, a polarization model is formed. The reconstructed terminal voltage is calculated based on the polarization model.

[0076] Specifically, the expression for the polarization model is:

[0077] ;

[0078] in, This indicates the degree of lithium intercalation on the positive electrode surface. Indicates the degree of lithium intercalation on the negative electrode surface. This represents the equivalent coefficient for the deviation in lithium intercalation degree of the positive electrode. This represents the equivalent coefficient for the deviation of lithium intercalation degree in the negative electrode. This indicates the current under the current constant current condition. Indicates the reconfiguration terminal voltage. This represents the residual polarization voltage at the i-th multiplier.

[0079] It should be noted that during the constant current charge-discharge process of a lithium battery, lithium ions diffuse within the active particles of the positive and negative electrodes, causing a deviation between the surface lithium intercalation degree and the average lithium intercalation degree. This deviation is related to the magnitude and direction of the current, and can therefore be characterized by an equivalent coefficient for the positive and negative electrode lithium intercalation degree deviation, which is linearly related to the current. Based on this, this method uses the average lithium intercalation degree of the positive and negative electrodes obtained in the aforementioned steps, combined with the current under the current conditions, to calculate the surface lithium intercalation degree of the positive and negative electrodes, thereby achieving an indirect estimation of the lithium ion concentration on the solid phase surface.

[0080] S6. Based on constant current charge and discharge data at multiple rates, identify the model parameters of the polarization model. The model parameters include the equivalent coefficient of the positive and negative electrode lithium intercalation deviation and the residual polarization voltage at each rate, and obtain the surface lithium intercalation estimation model.

[0081] Specifically, the particle swarm optimization algorithm is used to identify the parameters of the polarization model, and the expression of the fitness function used for identification is as follows:

[0082] ;

[0083] in, This represents the fitness function, and the total number of multipliers. This represents the measured terminal voltage.

[0084] It should be noted that the measured current and battery state-of-charge sequences at various rates are input into the polarization model to obtain the reconstructed terminal voltage under the corresponding candidate parameters. The mean square error between the reconstructed terminal voltage and the measured terminal voltage is used as the fitness function. The particle swarm optimization algorithm iteratively updates the particle velocity and position based on the individual optimal position and the swarm optimal position until the maximum number of iterations is reached. The position of the particle with the smallest fitness value is taken as the joint identification result for multiple operating conditions.

[0085] like Figure 4 As shown, taking the parameter identification results at 0.1C and 2.0C rates as examples, the fitted values ​​of the reconstructed terminal voltage curve and the experimental values ​​of the measured terminal voltage curve agree well across the entire SOC range. Figure 4 Mean square error in (a) , Figure 4 Mean square error in (b) , Figure 4 Mean square error in (c) , Figure 4 Mean square error in (d) All mean square errors were within a reasonable range, verifying the accuracy of the polarization model and the effectiveness of the parameter identification method. Through the above multi-rate joint identification, the polarization model output maintained a high degree of consistency with the actual charge and discharge data. The obtained model parameters can reflect the polarization characteristics under different operating conditions, providing a basis for estimating the lithium-ion concentration on the solid surface of the battery without disassembly. In addition, the green reference value curve and the red experimental value curve basically overlapped at 0.1C, indicating that the battery polarization effect was weak at low rates, and the terminal voltage was approximately equal to the open-circuit voltage. At 2.0C, the green reference value curve and the red experimental value curve deviated significantly, indicating that the polarization voltage increased significantly with increasing rate, further verifying the necessity of introducing residual polarization voltage.

[0086] S7. Obtain the maximum solid-phase lithium-ion concentration of the positive and negative electrode materials, and output the surface lithium intercalation degree of the positive and negative electrodes through the surface lithium intercalation degree estimation model; calculate the solid-phase surface lithium-ion concentration based on the maximum solid-phase lithium-ion concentration and the surface lithium intercalation degree of the positive and negative electrodes.

[0087] Specifically, the lithium-ion concentration on the solid surface is calculated using the following formula:

[0088] ;

[0089] in, This indicates the lithium-ion concentration on the solid phase surface of the positive electrode. This indicates the lithium-ion concentration on the surface of the negative electrode solid phase. This indicates the maximum solid-phase lithium-ion concentration at the positive electrode. This indicates the maximum solid-phase lithium-ion concentration at the negative electrode.

[0090] It is easy to understand that the maximum solid-phase lithium-ion concentration is an intrinsic parameter of the positive and negative electrode materials, which comes from the material's own physical property data and can be obtained through literature data.

[0091] Taking the estimation results of lithium-ion concentration on the solid surface of the positive and negative electrodes at different rates as an example: Figure 5 As shown in (a), the lithium-ion concentration on the solid phase surface of the positive electrode gradually decreases with increasing SOC and is lower than the average lithium-ion concentration of the positive electrode under charging conditions; Figure 5 As shown in (b), under discharge conditions, the lithium-ion concentration on the solid phase surface of the positive electrode gradually decreases with increasing SOC and remains higher than the average lithium-ion concentration of the positive electrode; Figure 5 As shown in (c), under charging conditions, the lithium-ion concentration on the solid phase surface of the negative electrode gradually increases with increasing SOC and is higher than the average lithium-ion concentration of the negative electrode; Figure 5 As shown in (d), under discharge conditions, the lithium-ion concentration on the solid surface of the negative electrode gradually increases with increasing SOC and remains lower than the average lithium-ion concentration of the negative electrode. The offset direction is consistent with the current direction, which conforms to the physical law of concentration polarization under constant current conditions. At the same SOC, the higher the rate, the greater the deviation of the lithium-ion concentration on the solid surface from the average lithium-ion concentration, indicating that the degree of concentration polarization increases with increasing rate. The above results show that the equivalent coefficient of the positive and negative electrode lithium intercalation deviation can effectively characterize the linear change law of concentration polarization with rate, and the surface lithium intercalation estimation model has rationality and consistency under different rate conditions.

[0092] The above are merely specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A method for estimating lithium-ion concentration on the solid surface of a lithium battery without disassembly, characterized in that, Includes the following steps: S1. Obtain constant current charge and discharge data of lithium battery at multiple rates, wherein the constant current charge and discharge data includes time data, voltage data, current data and capacity data, and obtain the rated capacity of lithium battery; S2. Based on the capacity data and the rated capacity, calculate the battery state of charge at each rate to obtain the corresponding curve of battery state of charge and voltage at each rate; S3. Select the lowest rate among multiple rates, obtain the charging voltage curve and the discharging voltage curve from the constant current charging and discharging data of the lowest rate, and construct a reference open circuit voltage curve based on the average value of the charging voltage curve and the discharging voltage curve. The reference open circuit voltage curve is used to characterize the relationship between the voltage of the lithium battery in equilibrium state and the state of charge of the battery. S4. Obtain the equilibrium potential curves of the positive and negative electrode materials, and establish a linear mapping relationship between the battery state of charge and the average degree of lithium intercalation based on the equilibrium potential curves, and calculate the reconstructed open circuit voltage; based on the reference open circuit voltage curve, identify the linear mapping parameters between the battery state of charge and the average degree of lithium intercalation. S5. Based on the electrochemical characteristics of lithium batteries under constant current conditions, a concentration polarization voltage caused by lithium intercalation deviation is introduced on the basis of the reconstructed open circuit voltage, and together with the remaining polarization voltage, a polarization model is formed. The reconstructed terminal voltage is calculated based on the polarization model. S6. Based on constant current charge and discharge data at multiple rates, identify the model parameters of the polarization model, including the equivalent coefficient of positive and negative electrode lithium intercalation deviation and the residual polarization voltage at each rate, to obtain the surface lithium intercalation estimation model. S7. Obtain the maximum solid-phase lithium-ion concentration of the positive and negative electrode materials, and output the surface lithium intercalation degree of the positive and negative electrodes through the surface lithium intercalation degree estimation model; calculate the solid-phase surface lithium-ion concentration based on the maximum solid-phase lithium-ion concentration and the surface lithium intercalation degree of the positive and negative electrodes.

2. The method for estimating lithium-ion concentration on the solid surface of a lithium battery under non-disassembly conditions according to claim 1, characterized in that, In step S2, the battery state of charge is calculated using the following formula: ； in, express The state of charge of the battery at any given time. Indicates the initial state of battery charge. This indicates the cumulative charging and discharging capacity at any given time. This indicates the actual total usable capacity of the battery under the current operating conditions.

3. The method for estimating lithium-ion concentration on the solid surface of a lithium battery under non-disassembly conditions according to claim 1, characterized in that, In step S3, the expression for the reference open-circuit voltage curve is: ； in, Indicates the reference open-circuit voltage. The constant current charging voltage curve represents the lowest charging rate. The constant current discharge voltage curve represents the lowest discharge rate.

4. The method for estimating lithium-ion concentration on the solid surface of a lithium battery under non-disassembly conditions according to claim 1, characterized in that, In step S4, the reconstructed open-circuit voltage is calculated using the following formula: ； in, This indicates the average degree of lithium intercalation in the positive electrode. This indicates the average degree of lithium intercalation in the negative electrode. express The boundary value of lithium intercalation degree at the positive electrode at that time. express The boundary value of lithium intercalation degree at the positive electrode at that time. The boundary value of the negative electrode lithium intercalation degree is represented at that time. The boundary value of the negative electrode lithium intercalation degree is represented at that time. Indicates the reconfigured open-circuit voltage. This represents the positive electrode equilibrium potential function. This represents the negative electrode equilibrium potential function.

5. The method for estimating lithium-ion concentration on the solid surface of a lithium battery under non-disassembly conditions according to claim 4, characterized in that, A hybrid optimization algorithm combining differential evolution and local optimization is used to identify the linear mapping parameters between the battery's state of charge and average lithium intercalation degree. The objective function used for identification is expressed as follows: ； in, express Total number of sampling points This means solving a problem with the objective function as the minimum value. .

6. The method for estimating lithium-ion concentration on the solid surface of a lithium battery under non-disassembly conditions according to claim 1, characterized in that, In step S5, the expression for the polarization model is: ； in, This indicates the degree of lithium intercalation on the positive electrode surface. Indicates the degree of lithium intercalation on the negative electrode surface. This represents the equivalent coefficient for the deviation in lithium intercalation degree of the positive electrode. This represents the equivalent coefficient for the deviation of lithium intercalation degree in the negative electrode. This indicates the current under the current constant current condition. Indicates the reconfiguration terminal voltage. Indicates the first Residual polarization voltage at a certain rate.

7. The method for estimating lithium-ion concentration on the solid surface of a lithium battery under non-disassembly conditions according to claim 6, characterized in that, In step S6, the particle swarm optimization algorithm is used to identify the parameters of the polarization model, and the expression of the fitness function used for identification is as follows: ； in, Represents the fitness function. This indicates the total number of multipliers. This represents the measured terminal voltage.

8. The method for estimating lithium-ion concentration on the solid surface of a lithium battery under non-disassembly conditions according to claim 1, characterized in that, In step S7, the lithium ion concentration on the solid surface is calculated using the following formula: ； in, This indicates the lithium-ion concentration on the solid phase surface of the positive electrode. This indicates the lithium-ion concentration on the surface of the negative electrode solid phase. This indicates the maximum solid-phase lithium-ion concentration at the positive electrode. This indicates the maximum solid-phase lithium-ion concentration at the negative electrode.

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