Method for establishing semi-solid battery impedance model and parameter identification method of semi-solid battery

Abstract

The application provides a method for establishing a semi-solid battery impedance model and a method for identifying parameters of a semi-solid battery. The method for establishing a semi-solid battery impedance model comprises the following steps: determining the constituent items of the impedance model of the semi-solid battery, wherein the constituent items comprise an inductance item, an ohmic internal resistance item, and an electrochemical impedance item, and the electrochemical impedance item comprises a solid-liquid diffusion impedance, a solid-phase diffusion impedance, a double-layer impedance, a passivation layer impedance, and a contact impedance; based on mechanism analysis of an electrochemical reaction process inside the semi-solid battery, determining the expression of each impedance in the electrochemical impedance item of the semi-solid battery, wherein the expression of the solid-liquid diffusion impedance is determined by analyzing the electrochemical process of the solid-liquid parallel diffusion channel inside the semi-solid battery under the influence of electric field coupling and synergistic drag effect. The technical solution of the application can realize accurate modeling of the impedance model of the semi-solid battery and improve the accuracy of parameter identification of the semi-solid battery.

Description

Technical Field

[0001] This application relates to the field of battery analysis technology, specifically providing a method for establishing a semi-solid-state battery impedance model and a method for identifying parameters of a semi-solid-state battery. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the core position of power batteries in the overall vehicle cost, performance, and safety has become increasingly prominent. In recent years, the sales and penetration rate of new energy vehicles have continued to increase, and the industry has put forward higher requirements for battery systems: on the one hand, higher energy density is needed to improve range, and on the other hand, higher safety is needed to reduce the risk of thermal runaway, while also taking into account fast charging capability and reliability throughout the entire life cycle. Against this backdrop, semi-solid-state batteries, due to their combination of high safety, high energy density, and structural / design flexibility, have gradually become an important technological direction for power batteries and have begun to be adopted in some vehicle models and application scenarios.

[0003] Compared with traditional liquid lithium-ion batteries, semi-solid batteries have significant differences in electrolyte morphology, interface structure, and mass transfer pathways. Therefore, directly using mature electrochemical models from traditional liquid batteries to describe the full-frequency electrochemical impedance response of semi-solid batteries often fails to accurately characterize key factors such as mass transfer processes, interfacial film effects, and contact characteristics in their solid-liquid coexisting electrolytes. This results in insufficient impedance spectrum fitting accuracy and unclear physical meaning, which in turn affects the reliability of parameter identification, aging assessment, and health status diagnosis. Summary of the Invention

[0004] This application provides a method for establishing a semi-solid-state battery impedance model through embodiments, including the following steps: S1. Based on the analysis of the semi-solid battery structure and electrochemical reaction mechanism, the constituent terms of the impedance model of the semi-solid battery are determined. The constituent terms include inductance, ohmic internal resistance and electrochemical impedance. The electrochemical impedance includes solid-liquid diffusion impedance, solid phase diffusion impedance, double layer impedance, passivation layer impedance and contact impedance. S2, Based on the mechanism analysis of the electrochemical reaction process inside the semi-solid battery, the expression of each impedance in the electrochemical impedance term of the semi-solid battery is determined. The expression of the solid-liquid diffusion impedance is determined by analyzing the electrochemical process of the solid-liquid parallel diffusion channel inside the semi-solid battery under the influence of electric field coupling and synergistic drag effect.

[0005] This application also provides a parameter identification method for semi-solid-state batteries through embodiments, the parameter identification method including the following steps: The measured impedance spectrum of the semi-solid-state battery under test is obtained by measurement. Based on the measured impedance spectrum, the optimal estimated values ​​of each parameter to be identified in the semi-solid battery impedance model are obtained by performing global optimization in the parameter search space with the goal of minimizing the deviation between the model-calculated impedance and the measured impedance. The semi-solid battery impedance model is determined by the aforementioned method for establishing the semi-solid battery impedance model.

[0006] The method for establishing the impedance model of a semi-solid battery provided in the embodiments of this application is a parameter identification method for semi-solid batteries. Based on the in-depth analysis of the "electric field coupling and cooperative dragging" mechanism of the solid-liquid ionization layer inside the semi-solid battery, combined with the constraints on the movement of lithium ions in the solid-liquid parallel diffusion channel, an expression is established to accurately describe its macroscopic homogeneous characteristics, thereby extracting the parameters to be identified that can characterize the solid-liquid parallel diffusion characteristics, thus effectively improving the accuracy of the analysis of the impedance characteristics of semi-solid batteries. Attached Figure Description

[0007] Figure 1 This is a flowchart of a method for establishing a semi-solid-state battery impedance model according to an embodiment of this application; Figure 2 This is a schematic diagram of the internal structure of a semi-solid-state battery. Figure 3 A schematic diagram of an idealized lithium-ion transport path in a semi-solid-state battery; Figure 4 A schematic diagram of the impedance model of a semi-solid-state battery; Figure 5 A schematic diagram showing the detailed transport path of lithium ions inside a semi-solid-state battery; Figure 6 A schematic diagram illustrating the principle of electric field coupling and synergistic drag effect in the solid-liquid diffusion parallel channels inside a semi-solid battery; Figure 7 This is a flowchart of a parameter identification method for semi-solid-state batteries provided according to an embodiment of this application; Figure 8 This is a photograph of the semi-solid-state battery used in Example 1. Figure 9 A schematic diagram of the parameters for impedance measurement in Example 1; Figure 10 This is a schematic diagram illustrating the disassembly and measurement of the semi-solid-state battery under test in Example 1. Figure 11 This is a schematic diagram comparing the identification results with the measured results in Example 1. Detailed Implementation

[0008] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0009] Electrochemical impedance spectroscopy (EIS) is an important electrochemical characterization technique used in the analysis of battery electrochemical properties. It can separate and identify multi-scale processes within the battery at different frequency bands, such as interfacial contact-related responses in the high-frequency region, charge transfer and double-layer-related responses in the mid-frequency region, and ion diffusion and solid-phase mass transfer-related responses in the low-frequency region. EIS is widely used in battery mechanism analysis, material and structure design verification, aging mechanism research, and battery health status assessment.

[0010] Compared to traditional liquid lithium-ion batteries, semi-solid batteries exhibit significant differences in electrolyte morphology, interface structure, and mass transfer pathways. Their electrolytes are typically solid-liquid coexisting systems or composite systems of a solid framework and ionic conductors. Ions are transported collaboratively in polymer matrix microchannels and solid / liquid regions, making the dominant mechanisms of ion migration, diffusion, and interfacial reaction kinetics not entirely consistent with those of liquid systems. Therefore, directly using mature electrochemical models from traditional liquid batteries to describe the full-frequency electrochemical impedance response of semi-solid batteries will ignore the key influences of electrolyte diffusion and interface structure differences. Consequently, it is difficult to accurately characterize key factors such as mass transfer processes, interfacial film effects, and contact characteristics in their solid-liquid coexisting electrolytes, resulting in insufficient impedance spectrum fitting accuracy and unclear physical meaning, which in turn affects the reliability of parameter identification, aging assessment, and health status diagnosis.

[0011] Furthermore, in engineering applications, semi-solid batteries still require rapid diagnostic and consistency assessment capabilities for vehicle and battery management systems. This necessitates that impedance models not only accurately reflect physical processes but also possess characteristics such as identifiable parameters, computational feasibility, and closed-loop verification with experimental data.

[0012] In the current technology, modeling methods for electrochemical impedance spectroscopy of semi-solid-state batteries are still under development and generally face the following shortcomings: (1) It is difficult to uniformly describe the ion diffusion and migration behavior under the coexistence of solid and liquid phases, and the model has insufficient adaptability; (2) The impedance composition is not clearly separated, making it difficult to reliably extract the impedance contribution of each physical process from the experimental impedance spectrum, thus affecting parameter identification, lifespan, and health status assessment.

[0013] Therefore, there is a need for an electrochemical impedance spectroscopy modeling and parameter identification method for semi-solid batteries. This method should be able to establish an impedance expression with clear physical meaning based on the transport characteristics of solid-liquid coexisting electrolytes and multi-interface dynamics, and combine experimental data to achieve parameter identification and model verification. This would provide a reliable model tool to support the mechanism research, performance evaluation and health diagnosis of semi-solid batteries.

[0014] To address the aforementioned problems, this application proposes a method for establishing a semi-solid-state battery impedance model. The figure illustrates a flowchart of the method for establishing a semi-solid-state battery impedance model according to some embodiments of this application, such as... Figure 1 As shown, the method includes the following steps: S1. Based on the analysis of the structure and electrochemical reaction mechanism of the semi-solid battery, the total impedance expression of the semi-solid battery is determined. The total impedance of the semi-solid battery includes an inductance term, an ohmic internal resistance term, and an electrochemical impedance term. The electrochemical impedance term includes solid-liquid diffusion impedance, solid-phase diffusion impedance, double-layer impedance, passivation layer impedance, and contact impedance. S2, Based on the mechanism analysis of the electrochemical reaction process inside the semi-solid battery, the expression of each impedance in the electrochemical impedance term of the semi-solid battery is determined, wherein the solid-liquid diffusion impedance is determined by analyzing the electrochemical process involved in the solid-liquid coexistence ion transport system inside the semi-solid battery.

[0015] The following provides a detailed explanation of the specific implementation process of steps S1 and S2.

[0016] <Step S1: Determine the total impedance expression for the semi-solid-state battery> Step S1 is used to analyze the internal structure and electrochemical reaction mechanism of the semi-solid-state battery in order to determine the specific composition of the impedance total impedance model used to characterize the impedance characteristics of the semi-solid-state battery.

[0017] On the one hand, in semi-solid-state batteries, the electrolyte is a polymer-based semi-solid material, typically composed of a polymer matrix and an ionic liquid. On the other hand, ions in semi-solid-state batteries are transported through tiny channels in the polymer matrix, resulting in a slower ion transport rate and a lower reaction rate compared to traditional liquid batteries. This leads to a significant difference in the diffusion patterns of the solid-liquid electrolyte in semi-solid-state batteries compared to those in traditional batteries. Therefore, it is necessary to conduct in-depth analysis of the corresponding electrochemical reaction mechanisms based on the internal structure of semi-solid-state batteries in order to establish a total impedance model that can accurately characterize both the external macroscopic properties and the internal microscopic reactions of semi-solid-state batteries.

[0018] Figure 2 The internal structure of a semi-solid-state battery is shown, such as... Figure 2 As shown, a semi-solid cell is structurally composed of a positive electrode current collector (usually made of aluminum foil material Al), a positive electrode active layer Cathode (usually made of lithium nickel cobalt manganese oxide ternary material NCM), a separator, a negative electrode active layer Anode (usually made of silicon / carbon Si / C material), and a negative electrode current collector (usually made of copper foil material Cu).

[0019] The separator is generally made of polyethylene / polypropylene (PE / PP) material as a base. Solid electrolyte particles (such as lithium aluminum titanium phosphate, LATP) are carried on the surface of the separator and in the electrode pores. After the battery is injected with liquid electrolyte (lithium salt + organic solvent), the liquid electrolyte wets and fills the pores of the separator and the electrode, and together with the solid electrolyte particles, it forms a solid-liquid electrolyte layer (Solid-Liquid Electrolyte) that is a mixture of solid and liquid phases.

[0020] During the charging and discharging process of a semi-solid-state battery, electrons are mainly transported along the solid-phase conductive network of the positive and negative electrodes to the positive and negative current collectors, respectively. Ions migrate and diffuse within the solid-liquid electrolyte phase in the pores of the membrane and electrodes. When ions reach the surface of the active particles, a charge transfer reaction occurs at the interface between the positive and negative active layers, crossing the electric double layer and the passivation layer, thereby achieving... Ions deintercalate / intercalate at the positive and negative electrodes, and then undergo solid-phase diffusion within the active particles.

[0021] The above The migration and diffusion processes of ions can be achieved through... Figure 3 The idealized lithium-ion transport path of the semi-solid-state battery is shown, where all lithium-ion transport paths can be equivalently replaced by the transport path of a single lithium ion at the farthest active particle. The sum of the equivalent impedances of all electrochemical reactions occurring in this path is the electrochemical impedance of the semi-solid-state battery.

[0022] Based on the above analysis of the solid-state battery structure and electrochemical process, the components of the impedance model for semi-solid-state batteries can be determined, such as... Figure 4 As shown, the impedance model of a semi-solid-state battery can be composed of an inductance term, an ohmic internal resistance term, and an electrochemical impedance term. The electrochemical impedance term further includes solid-liquid diffusion impedance, solid-phase diffusion impedance, double-layer impedance, passivation layer impedance, and contact impedance. Therefore, the impedance model of a semi-solid-state battery can be expressed by the total impedance expression shown in equation (1). Characterization: , In the above formula, Angular frequency, The inductance value generated by the metal component. The inductance term is in complex form. For the ohmic internal resistance term, For contact resistance, For passivation layer impedance, It is the double-layer impedance. For solid-liquid diffusion resistance, This represents the solid-phase diffusion impedance.

[0023] in, and The specific expressions for the impedances constituting the electrochemical impedance terms can be determined by measuring the metal components and the basic geometry of the semi-solid-state battery. The specific expressions for the impedances constituting the electrochemical impedance terms need to be derived in step S2 based on further analysis and derivation of the electrochemical reaction mechanism inside the semi-solid-state battery.

[0024] <Step S2: Determine the expressions for each impedance term in the electrochemical impedance term of the semi-solid-state battery> A. Determining the expression for solid-liquid diffusion impedance based on electric field coupling and synergistic drag effect in solid-liquid parallel diffusion channels. Figure 5 The detailed transport path of lithium ions inside a semi-solid battery is shown. The diffusion path of lithium ions in the solid-liquid electrolyte layer can be regarded as a special "solid-liquid parallel diffusion path". Therefore, in order to obtain an accurate expression for the solid-liquid diffusion impedance, it is necessary to analyze the electrochemical process of lithium ions through the above-mentioned solid-liquid parallel diffusion path as accurately as possible.

[0025] In existing technologies, the impedance characteristics analysis of mixed electrolyte layers generally involves weighted summation of the diffusion coefficients of the various components constituting the mixed electrolyte layer to obtain an equivalent diffusion coefficient. Furthermore, a variable cross-section pipe model can be set up based on the different proportions of the mixed components at different locations to refine the electrochemical characteristics of lithium ions diffusing to different positions within the mixed electrolyte layer. However, the applicant has found that simply using the above equivalent model cannot accurately describe the impedance characteristics of the "solid framework + ionic conductor composite system" present in semi-solid batteries. The specific reasons can be found in [link to relevant documentation]. Figure 6 .

[0026] like Figure 6 As shown, when current is injected into the semi-solid battery and passes through the solid-liquid electrolyte layer, lithium ions are transported in both the solid and liquid phases. The ion transport speed is faster in the solid electrolyte transport channel, resulting in local ion stacking, forming a concentration gradient and causing concentration polarization. This generates an additional electric field in the solid phase channel. Due to the diffusion mechanism of the solid and liquid phases in parallel, the solid and liquid phase channels share this additional electric field, thereby dragging the slower-transmitting ions in the liquid phase channel. Ultimately, this microscopic electric field coupling and synergistic dragging mechanism forms a macroscopic synergistic diffusion effect.

[0027] Obviously, using only a conventional variable cross-section pipe model cannot accurately characterize the above-mentioned synergistic mechanism. Therefore, in the embodiments of this application, an accurate expression for the solid-liquid diffusion impedance is established based on the electric field coupling and synergistic drag effect existing in the solid-liquid parallel diffusion channel.

[0028] In some specific embodiments, the precise expression for the solid-liquid diffusion impedance in a semi-solid battery can be established through the following steps: First, based on the analysis of the electric field coupling and synergistic drag effect, the constraint conditions that ions must satisfy for diffusion in the solid-liquid parallel diffusion channel are determined. Then, based on the electric field coupling and synergistic drag effect and under the constraint conditions, the expression for the solid-liquid diffusion impedance is derived.

[0029] Specifically, based on the solid-liquid mixing characteristics of the solid-liquid electrolyte layer in a semi-solid battery, and combined with the physical laws governing ion diffusion within the semi-solid battery, the constraint conditions that ions must satisfy for diffusion in the solid-liquid parallel diffusion channel can be determined. In the embodiments of this application, the constraint conditions include at least the following: 1) Constraints on macroscopic homogeneity Because the liquid electrolyte in the solid-liquid electrolyte layer wets and fills the spaces between the solid electrolyte particles, forming a composite system of solid framework and ion conductor, the solid-phase network and liquid-phase network completely overlap in space within the solid-liquid parallel diffusion channel. Therefore, the plate and transport layer can be considered equivalent to a one-dimensional continuous medium. In the solid-liquid parallel diffusion channel, along the diffusion direction (i.e., the thickness direction of the semi-solid battery, as shown in the figure)... (Axis representation) Positions at the same distance exhibit the same macroscopic characteristics.

[0030] 2) Isopotential gradient constraint condition In a solid-liquid parallel diffusion channel, the two channels have the same starting and ending points along the diffusion direction, forming a parallel circuit macroscopically. At the same time, if there is a difference in potential between the two channels microscopically, it will be instantly smoothed out in the transverse direction (perpendicular to the diffusion direction). Therefore, in a solid-liquid parallel diffusion channel, the solid electrolyte and the liquid electrolyte share the same potential gradient along the diffusion direction.

[0031] 3) Local thermodynamic equilibrium constraints Within the solid-liquid parallel transport channel, the contact surface area between the solid and liquid phases is extremely large, and the ion transphase transport time is extremely short, resulting in a very fast ion exchange rate between the solid and liquid phases. Therefore, within the solid-liquid parallel transport channel, the ion concentration is the same at all positions along the same distance in the diffusion direction.

[0032] After determining the above constraints, the expression for the solid-liquid diffusion impedance can be derived. Specifically, the derivation process includes the following steps: Step 1: Based on the electric field coupling and synergistic drag effect, and under the constraints of the aforementioned conditions, establish a general expression for the AC fluctuation part of the macroscopic homogeneous electric field in the solid-liquid parallel diffusion channel.

[0033] First, based on the Nernst equation and considering the additional electric field generated in the solid-phase channel within the solid-liquid parallel diffusion channel, the lithium-ion flux in the solid-phase channel is expressed as a diffusion flux component and an electromigration flux component: (1), (1) In the formula, , , , These represent the lithium-ion flux, lithium-ion diffusion coefficient, lithium-ion concentration, and potential of the solid-phase channel, respectively. The position variable is along the diffusion direction. The number of lithium-ion charges. It is Faraday's constant. The gas constant is... For temperature.

[0034] Lithium-ion current density in solid-phase channels and conductivity They are respectively: (2), (3), Combining equations (1), (2), and (3), we can obtain: (4).

[0035] Considering that the solid-liquid parallel diffusion channel satisfies the isopotential constraint condition, at any position in the diffusion direction At this point, the potential of the liquid phase channel in the solid-liquid parallel diffusion channel. The potential of the solid-state channel and macroscopic homogeneous potential satisfy: (5), Based on the Nernst equation and considering the drag effect on lithium ions within the liquid phase channel, the lithium ion current density within the liquid phase channel is... This is represented as the diffusion flow portion and the electric field-driven flow portion: (6), In formula (6), , , These represent the lithium-ion diffusion coefficient, lithium-ion concentration, and electrical potential of the liquid phase channel, respectively. Combining equations (4), (5), and (6), we can obtain: (7), in, The conductivity of the liquid phase channel is denoted as .

[0036] Total lithium-ion current density along the diffusion direction in the solid-liquid parallel diffusion channel for: (8).

[0037] Will , Using macroscopic homogeneous potential respectively express: (9), (10) Combining equations (8), (9), and (10), we can obtain: (11).

[0038] Based on the local thermodynamic equilibrium constraint, the lithium-ion concentration in the solid phase channel of the solid-liquid parallel diffusion channel... Lithium ion concentration in the liquid phase channel and the macroscopic homogeneous lithium-ion concentration of the solid-liquid parallel diffusion channel. They can be considered the same, that is: (12), Simultaneously define the equivalent conductivity of the solid-liquid parallel diffusion channel. : (13) Substituting equations (12) and (13) into equation (11), we can obtain the macroscopic homogeneous electric field expression for the solid-liquid parallel diffusion channel, including the total lithium-ion current density of the solid and liquid phase channels. The resulting ohmic electric field portion, and the concentration electric field portion generated by concentration polarization caused by lithium ion stacking in the aforementioned solid-phase channel: (14).

[0039] The total lithium-ion current density, macroscopic homogeneous lithium-ion concentration, and macroscopic homogeneous potential of the solid-liquid parallel diffusion channel are expressed in frequency domain form: (15) (16) (17) in, , They are respectively , The steady-state part, , , They are respectively , , The complex amplitude of the alternating wave component, It is the imaginary unit.

[0040] Substituting equations (15), (16), and (17) into equation (14), we get: (18).

[0041] After separating the steady-state term and the AC fluctuation term, taking the AC fluctuation term, we have: (19) Simplifying, we get: (20).

[0042] Equation (20) is the general expression for the AC fluctuation part of the macroscopic homogeneous electric field in the solid-liquid parallel diffusion channel, which is established considering electric field coupling and synergistic drag effect and under corresponding constraints.

[0043] Step 2: Based on the distribution of the solid-liquid parallel channels along the thickness direction inside the semi-solid battery, determine the expression for the macroscopic homogeneous concentration difference of lithium ions in each sub-region constituting the solid-liquid parallel channels.

[0044] During discharge, lithium ions move along the thickness direction ( Figure 5 (As shown by the arrow on the x-axis) it moves from the negative electrode to the positive electrode, and passes through the diaphragm during the movement, therefore, as... Figure 5 As shown, the solid-liquid parallel diffusion channel is located between the negative electrode and the membrane, with a thickness of [missing information]. The sub-region is called the first parallel sub-region, located between the separator and the positive electrode, with a thickness of [missing information]. The sub-region is called the second parallel sub-region, which will be located between the two parallel sub-regions and has a thickness of [missing information]. The membrane portion is called the membrane sub-region. It can be understood that, due to the structural limitations of the membrane, almost only liquid-phase diffusion of lithium ions occurs within the membrane sub-region.

[0045] According to the bipolar transport theory, the lithium-ion concentration in a solid-liquid parallel diffusion channel can be expressed by Fick's law: (twenty one), In the formula, , These are the lithium-ion synergistic diffusion coefficients for the first and second parallel sub-regions, respectively, reflecting the diffusion characteristics exhibited by the synergistic effect of the solid-liquid electrolyte in these two sub-regions. Let be the lithium-ion diffusion coefficient of the membrane sub-region. Considering that almost only liquid-phase diffusion exists in this sub-region, it can be... Considered as equal, , These represent the fluctuations in lithium-ion concentration in the left and right parallel channel regions, respectively. This represents the fluctuation in lithium-ion concentration in the diaphragm region.

[0046] Solving for the concentrations in the three sub-regions above, we get: (twenty two), (twenty three), (twenty four), in, , , These are the diffusion wavenumbers of the first parallel sub-region, the diaphragm sub-region, and the second parallel sub-region, respectively.

[0047] The boundary conditions for solid-liquid parallel diffusion channels include concentration continuity conditions and boundary flux conditions, among which, The conditions for continuous concentration are: (25), (26).

[0048] The boundary flux condition is: (27) (28) (29) (30) Among them, such as Figure 5 As shown, , , The thicknesses of the first parallel sub-region, the diaphragm sub-region, and the second parallel sub-region are respectively.

[0049] Furthermore, substituting the boundary conditions into the concentration expression, we obtain the specific expressions for each intermediate variable as shown in Table 1 below: Table 1. Specific expressions for each intermediate variable in the solid-liquid parallel diffusion channel. This yields the macroscopic homogeneous concentration difference expression for each sub-region constituting the solid-liquid parallel channel (i.e., the concentration difference between the end and beginning points of each sub-region), where... The macroscopic homogeneous lithium-ion concentration difference in the first parallel sub-region is: (31), The macroscopic homogeneous concentration difference of lithium ions in the membrane sub-region is: (32), The macroscopic homogeneous lithium-ion concentration difference in the second parallel sub-region is: (33).

[0050] Step 3: Based on the results of Step 1 and Step 2, determine the expression for the solid-liquid diffusion impedance of the semi-solid battery.

[0051] Specifically, first, integrate equation (20) and divide it by the current term to obtain the general formula for the unit area impedance of each sub-region of the solid-liquid parallel diffusion channel: (34), Substitute equations (31), (32), and (33) into equation (34) and divide by the cross-sectional area of ​​the battery. The impedance expressions for each sub-region of the solid-liquid parallel diffusion channel can be obtained, where the impedance expression for the first parallel sub-region is: (35), in, The equivalent conductivity of the first parallel sub-region is , These are the lithium-ion diffusion coefficients of the solid-phase channel and the liquid-phase channel in the first parallel sub-region, respectively.

[0052] The impedance expression for the intermediate septum region is: (36) in, The conductivity of the diaphragm subregion; The impedance expression for the second parallel sub-region is: (37) in, The equivalent conductivity of the second parallel sub-region, , These are the lithium-ion diffusion coefficients of the solid-phase channel and the liquid-phase channel in the second parallel sub-region, respectively.

[0053] Finally, we obtain the expression for the solid-liquid diffusion impedance: (38) in, , , The expressions are (35), (36), and (37), respectively, and the expressions of the intermediate variables are shown in Table 1.

[0054] In the solid-liquid diffusion impedance expressions shown in equations (35) to (38), the thickness and cross-sectional area of ​​each sub-region can be obtained from the technical manual of the semi-solid-state battery, or they can be obtained by disassembling and measuring the semi-solid-state battery under experimental conditions. Therefore, the parameters to be identified are... , , , , , , , , , As can be seen, in addition to the usual solid-phase, liquid-phase, and membrane-related parameters to be identified, the cooperative diffusion coefficient also appears in the expression for solid-liquid diffusion impedance. , and equivalent conductivity , These four items are the parameters to be identified related to electric field coupling and synergistic drag effect, which are used to reflect the influence of the aforementioned electric field coupling and synergistic drag effect on the solid-liquid parallel diffusion system.

[0055] B. Expressions for other diffusion impedances Since the electrochemical reaction mechanisms involved in the solid-phase diffusion impedance, double layer, passivation layer diffusion impedance, and contact impedance in semi-solid-state batteries are similar to those in conventional lithium-ion batteries, the expressions for the solid-phase diffusion impedance, double layer, passivation layer diffusion impedance, and contact impedance can be determined by referring to the impedance model of lithium-ion batteries in the embodiments of this application.

[0056] For example, in some embodiments, the expression for solid-phase diffusion impedance is: , In the above formula, These represent the negative and positive electrodes, respectively. , These are the solid-phase diffusion impedances of the negative and positive electrodes, respectively. For correction factor, , , These are the specific surface area, electrode thickness, and electrode area of ​​the negative or positive electrode, respectively. The solid-phase diffusion coefficient of lithium ions is the coefficient of diffusion between the positive and negative electrodes. , These represent the initial and maximum lithium-ion concentrations at the negative and positive electrodes, respectively. The radius of the active material particles for the negative or positive electrode.

[0057] Will and By combining these expressions, we can obtain the solid-phase diffusion impedance expression.

[0058] For example, in some embodiments, the double-layer diffusion impedance can also be obtained through the negative double-layer diffusion impedance. and positive electrode double layer diffusion impedance The result of merging is that, , The expressions are as follows: , , In the above formula, , , These are the specific surface area, thickness, and area of ​​the negative electrode, respectively. It is a negative electrode double-layer capacitor. The negative electrode exchange current density, The negative electrode electrochemical reaction constant, This represents the lithium-ion concentration in the inorganic layer near the SEI film in the inner electric double layer. This represents the lithium-ion concentration on the surface of the negative electrode active particles. This represents the maximum lithium-ion concentration of the negative electrode active particles. , , These are the specific surface area, thickness, and area of ​​the positive electrode, respectively. It is a positive double-layer capacitor. The positive electrode exchange current density, The positive electrode electrochemical reaction constant, This represents the lithium-ion concentration in the inorganic layer near the CEI film in the inner electric double layer. This represents the lithium-ion concentration on the surface of the positive electrode active particles. This represents the maximum lithium-ion concentration of the positive electrode active particles.

[0059] Will , By combining these expressions, we can obtain the double-layer diffusion impedance expression.

[0060] For example, in some embodiments, the passivation layer diffusion resistance Impedance can be diffused through the inorganic layer (negative electrode) of the SEI film. diffusion resistance of inorganic layer (positive electrode) of CEI film The result of merging is that, , The expression is: In the above formula, , , , These represent the thickness, conductivity, capacitance, and lithium-ion diffusion coefficient of the inorganic layer of the SEI film, respectively. , , , These represent the thickness, conductivity, capacitance, and lithium-ion diffusion coefficient of the inorganic layer of the CEI film, respectively.

[0061] For example, in some embodiments, the contact impedance can be expressed by the following formula: , in, and These are contact resistance and contact capacitance, respectively.

[0062] By following the steps above, the impedance model of the semi-solid battery can be established.

[0063] Some embodiments of this application also provide a method for parameter identification of semi-solid-state batteries, such as... Figure 7 As shown, the parameter identification method includes the following steps: The first step is to measure and obtain the measured impedance spectrum of the semi-solid-state battery under test; The second step involves obtaining the optimal estimates of each parameter to be identified in the semi-solid-state battery impedance model by performing global optimization within the parameter search space, with the goal of minimizing the deviation between the model-calculated impedance and the measured impedance. The semi-solid-state battery impedance model is determined using the aforementioned method for establishing the semi-solid-state battery impedance model.

[0064] Specifically, the test can begin by applying an AC excitation within a preset frequency range (e.g., 0.01 Hz to 10 kHz) to the semi-solid-state battery under test and performing an EIS test to obtain the measured impedance spectrum. Based on this, search algorithms such as genetic algorithms and particle swarm optimization can be used to select the parameters to be identified in the semi-solid-state battery impedance model established earlier as search variables and perform global optimization within a preset parameter space. The fitness function used in the search algorithm is usually defined as the root mean square error between the model-calculated impedance and the measured impedance. The search process iterates continuously until the parameter combination that minimizes the fitness function is found, which can then be used as the identification result of the various parameters of the semi-solid-state battery.

[0065] In addition, in some optional embodiments, after obtaining the measured impedance spectrum, the measured impedance spectrum can be analyzed using DRT analysis methods known to those skilled in the art (such as Tikhonov regularization combined with L-curve method, or using existing toolkits such as DRTtools) to obtain DRT curves corresponding to different electrochemical processes. The DRT curves can provide preliminary estimates of the time constants and resistances of each RC element in the impedance model, and can be used to determine the model structure (such as the number of RC parallel elements) and the boundary range of subsequent parameter searches.

[0066] Example 1 Example 1 is used to verify the accuracy of the semi-solid battery impedance model established by the method of this application. The semi-solid battery under test has a nominal voltage of 3.7V, a battery capacity of 12AH, a charging cutoff voltage of 4.2V, a minimum cutoff voltage of 2.8V, a ternary cathode material, and a graphite anode material. Figure 8 This is a photograph of the semi-solid-state battery under test.

[0067] First, the semi-solid-state battery under test was measured using an impedance analyzer to obtain the measured impedance spectrum. The impedance measurement parameter settings are detailed in [link to impedance analysis]. Figure 9 After completing the impedance measurement, the semi-solid-state battery under test was further disassembled to measure its internal dimensional parameters. Figure 10 The disassembly and measurement of the tested semi-solid-state battery are shown below. Positive and negative electrode length: 27cm Positive and negative electrode width: 9.8cm Area: 0.02646m² 2 , Negative electrode thickness: 180 / piece, Number of negative electrodes: 16 Single copper foil thickness: 21 , Diaphragm thickness: 12.5 , Positive electrode thickness: 171 / piece, Number of positive electrodes: 15 pieces Aluminum foil thickness: 19 .

[0068] The measured battery dimensions, area, thickness, and other parameters are substituted into the semi-solid battery impedance model established by the aforementioned method. Each parameter to be identified in the model is used as a search parameter, and the particle swarm optimization algorithm is used to search for the result that minimizes the error between the impedance spectrum calculated by the model and the measured impedance spectrum.

[0069] The following are some of the parameter settings for the search algorithm: Population size N=50, maximum number of iterations ger=100; Learning factors c1=2, c2=2; The dynamic inertia weight w decreases linearly from 0.905 to 0.4; Velocity boundary setting: ±15% of the position boundary span; Random mutation policy threshold: 0.7.

[0070] Among the parameters to be identified, those identical to those in conventional lithium-ion batteries can be set by referring to existing lithium-ion battery parameter identification methods. For parameters added due to electric field coupling and synergistic drag effects in solid-liquid parallel diffusion, [further details are needed]. , and Their search space ranges are as follows: [ , ]、[ , ]、[ , ]、[ , ].

[0071] Figure 11 The results show a comparison between the impedance spectrum generated using the parameters obtained from the search and the measured impedance spectrum (the solid-liquid diffusion portion and the solid-phase diffusion portion obtained by DRT processing). After error analysis, the MAE of both is 0.05Ω and the MRE is 5.8%, proving that the method provided in this application can effectively achieve accurate estimation of the impedance of semi-solid cells.

[0072] The specific embodiments of this application have been described in detail above. For those skilled in the art, several improvements and modifications can be made to this application without departing from the principle of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for establishing a semi-solid-state battery impedance model, characterized in that, Includes the following steps: S1. Based on the analysis of the semi-solid battery structure and electrochemical reaction mechanism, the constituent terms of the impedance model of the semi-solid battery are determined. The constituent terms include inductance, ohmic internal resistance and electrochemical impedance. The electrochemical impedance includes solid-liquid diffusion impedance, solid phase diffusion impedance, double layer impedance, passivation layer impedance and contact impedance. S2, Based on the mechanism analysis of the electrochemical reaction process inside the semi-solid battery, the expression of each impedance in the electrochemical impedance term of the semi-solid battery is determined. The expression of the solid-liquid diffusion impedance is determined by analyzing the electrochemical process of the solid-liquid parallel diffusion channel inside the semi-solid battery under the influence of electric field coupling and synergistic drag effect.

2. The method for establishing the semi-solid-state battery impedance model according to claim 1, characterized in that, The electrochemical process of the solid-liquid parallel diffusion channel inside the semi-solid battery under the influence of electric field coupling and synergistic drag effect is analyzed as follows: Based on the analysis of the electric field coupling and synergistic drag effect, the constraint conditions that ions must satisfy for diffusion in the solid-liquid parallel diffusion channel are determined, and the expression for the solid-liquid diffusion impedance is derived.

3. The method for establishing the semi-solid-state battery impedance model according to claim 2, characterized in that, The constraints include: The macroscopic homogeneity constraint condition is used to constrain the same macroscopic characteristics at all positions along the same distance in the diffusion direction in a solid-liquid parallel diffusion channel. The equipotential gradient constraint condition is used to constrain the solid electrolyte and liquid electrolyte to share the same potential gradient along the diffusion direction in a solid-liquid parallel diffusion channel. Local thermodynamic equilibrium constraint conditions are used to ensure that the ion concentration is the same at all positions along the same distance in the diffusion direction in a solid-liquid parallel transport channel.

4. The method for establishing the semi-solid-state battery impedance model according to claim 3, characterized in that, The expression for the solid-liquid diffusion impedance includes the impedance expression for the first parallel sub-region from the battery negative electrode to the separator in the solid-liquid parallel diffusion channel, the impedance expression for the second parallel sub-region from the separator to the battery positive electrode, and the impedance expression for the separator sub-region between the two parallel sub-regions.

5. The method for establishing the semi-solid-state battery impedance model according to claim 4, characterized in that, The expression for the solid-liquid diffusion impedance is derived through the following steps: Step 1: Based on the electric field coupling and synergistic drag effect, and under the constraints of the aforementioned conditions, establish a general expression for the AC fluctuation part of the macroscopic homogeneous electric field in the solid-liquid parallel diffusion channel. Step 2: Based on the distribution of the solid-liquid parallel channels along the thickness direction inside the semi-solid battery, determine the expression for the macroscopic homogeneous concentration difference of lithium ions in each sub-region constituting the solid-liquid parallel channels. Step 3: Based on the results of Step 1 and Step 2, determine the expression for the solid-liquid diffusion impedance of the semi-solid battery.

6. The method for establishing the semi-solid-state battery impedance model according to claim 5, characterized in that, In the expression for the solid-liquid diffusion impedance of the semi-solid battery, the parameters to be identified related to the electric field coupling and synergistic drag effect include: lithium-ion cooperative diffusion coefficient in the first parallel sub-region and equivalent conductivity The lithium-ion cooperative diffusion coefficient of the second parallel sub-region and equivalent conductivity .

7. The method for establishing the semi-solid-state battery impedance model according to claim 6, characterized in that, The impedance expressions for the first parallel sub-region, the diaphragm sub-region, and the second parallel sub-region in the solid-liquid parallel diffusion channel are as follows: ， ， ， in, , , The impedance expressions for the first parallel sub-region, the diaphragm sub-region, and the second parallel sub-region are respectively. Angular frequency, , , The thicknesses of the first parallel sub-region, the diaphragm sub-region, and the second parallel sub-region are respectively. , These are the lithium-ion diffusion coefficients of the solid-phase channel and the liquid-phase channel in the first parallel sub-region, respectively. The lithium-ion diffusion coefficient is the number of ions in the membrane sub-region. , These are the lithium-ion diffusion coefficients of the solid-phase channel and the liquid-phase channel in the second parallel sub-region, respectively. The conductivity of the diaphragm sub-region, The cross-sectional area of ​​the battery. , , The diffusion wavenumbers for the first parallel sub-region, the diaphragm sub-region, and the second parallel sub-region are respectively. , , , , , , , It is an intermediate variable.

8. A method for parameter identification of a semi-solid-state battery, characterized in that, Includes the following steps: The measured impedance spectrum of the semi-solid-state battery under test is obtained by measurement. Based on the measured impedance spectrum, the optimal estimated values ​​of each parameter to be identified in the semi-solid battery impedance model are obtained by performing global optimization in the parameter search space with the goal of minimizing the deviation between the model-calculated impedance and the measured impedance. The semi-solid battery impedance model is determined by the method for establishing the semi-solid battery impedance model as described in claim 1.

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