Lithium ion battery expansion force decoupling method

Abstract

The invention relates to a lithium ion battery expansion force decoupling method. The method comprises the following steps: S1, collecting battery data and signals including voltage, current, temperature, temperature rise and expansion force through a battery test platform; s2, extracting temperature and temperature rise data and signals, and calculating the thermal expansion force of the battery by combining the thermal expansion coefficient alpha of the battery; s3, extracting 0.05 C charging capacity and expansive force data of the battery, and defining a battery expansive force-capacity reference curve to represent lithium intercalation and deintercalation expansive force; s4, based on the capacity data of the battery under the charging multiplying power except the 0.05 C charging capacity, interpolation calculation is carried out through the battery expansibility-capacity reference curve; and S5, calculating expansion force change caused by additional side reaction of the battery according to the expansion force signal and data of the battery at any multiplying power in combination with the battery thermal expansion force and lithium intercalation and deintercalation expansion force calculated in the steps S2, S3 and S4, so as to determine the expansion force of the battery in each chemical reaction process and realize battery expansion force decoupling. The method is simple in step, easy to operate and high in reliability.

Description

Technical Field

[0001] This invention relates to the field of battery safety technology, and specifically to a method for decoupling the expansion force of lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries can effectively reduce environmental pollution and energy consumption. Battery mechanical behavior is a characteristic of battery health and safety. As an electrochemical-physical structure, lithium-ion batteries experience particle volume expansion and contraction during lithium insertion / extraction, generating diffusion-induced stress. In practice, the battery's expansion force is coupled with various chemical reaction processes such as lithium insertion state, temperature, and side reactions. When using battery expansion force signals for battery state estimation or fault detection, it is necessary to decouple the expansion forces of each chemical reaction process. Therefore, accurately decoupling the expansion forces of each battery component is crucial.

[0003] Existing methods for estimating battery state of charge, detecting lithium plating, and providing early warning of thermal runaway all utilize the measurable macroscopic external total expansion force signal of the battery. However, there is still no effective method to decouple the expansion force of a single chemical reaction process, especially research on decoupling the expansion forces of various battery components under conditions of multiple chemical reactions being coupled together. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a method for decoupling the expansion force of a lithium-ion battery, comprising the following steps: S1: Collect battery data and signals, including voltage, current, temperature, temperature rise, and expansion force, through the battery testing platform; S2: Extract temperature and temperature rise data and signals based on the battery data and signals collected in S1, and combine them with the battery thermal expansion coefficient. α Calculating the battery thermal expansion force, which refers to the change in expansion force caused by temperature rise during battery charging and discharging, specifically includes the following steps: S21: In order to accurately calculate the battery thermal expansion force, the thermal expansion coefficient of the battery at different SOCs was tested. Since the thermal expansion coefficients at different SOCs are relatively close, the average value of the thermal expansion coefficients at different SOCs, 0.054kN / ℃, was selected for calculation; SOC refers to the state of charge. S22: This utilizes the battery's thermal expansion force. F thermal Defined as the change in battery pressure caused by changes in battery temperature. F total Due to the influence of the battery's thermal expansion coefficient and state of charge (SOC), the thermal expansion force is positive when the temperature rises and negative when the temperature falls. The calculation formula is as follows: ; (1) In the formula:α The coefficient of thermal expansion of the battery. This refers to the temperature change of the battery during charging and discharging. S23: Calculate the battery thermal expansion force curve based on the battery temperature rise curve; S3: Based on the battery data collected in S1, extract the capacity and expansion force data of the battery at 0.05C charging, and define a battery expansion force-capacity baseline curve to characterize the lithium insertion / extraction expansion force: Define the benchmark interpolation function based on the expansion force curve corresponding to 0.05C: ; In the formula: y i This represents the function value of the expansion force change caused by the lithium insertion / extraction reaction in the battery at a specific capacity. x i Battery charging capacity Q chg or discharge capacity Q dis ; P ( x i () is the interpolation polynomial for the battery charge / discharge capacity; S4: Based on the battery capacity data at charging rates other than 0.05C, and through interpolation calculation using the battery expansion force-capacity baseline curve, this includes calculating the pure lithium insertion / extraction pressure increment during charging and discharging at each charging rate other than 0.05C. F li The curve of change is calculated using the following formula: ; (2) Where: Q chg This refers to the charging capacity. Q dis Discharge capacity; P ( Q chg () is the interpolation polynomial for battery charging capacity; P ( Q dis () is the interpolation polynomial for battery discharge capacity; F li,xC,CC The increment of pure lithium insertion / extraction pressure during charging corresponds to each charging rate other than the 0.05C charging capacity. F li The changing function value; F li,xC,DC The increment of pure lithium insertion / extraction pressure during discharge corresponding to each charging rate other than 0.05C charging capacity. F li The changing function value; S5: Based on the battery expansion force signal and data collected in S1 at any rate, and combined with the battery thermal expansion force and lithium insertion / extraction expansion force calculated in S2, S3, and S4, calculate the expansion force change caused by additional side reactions of the battery, thereby determining the expansion force of the battery in each chemical reaction process, and achieving decoupling of the battery expansion force. Specifically, this includes the following steps: S51: Define the concept of expansion force for each chemical reaction during battery charging and discharging: Battery pressure change F total Defined as the pressure increment during a single charge and discharge cycle of a battery, with a positive value for charging and a negative value for discharging, it reflects the degree of expansion or contraction of the battery's active material particles during the discharge process. Pure lithium insertion / extraction pressure increment F li Defined as the pressure change caused solely by the extraction and insertion of lithium ions within the active material particles during battery charging and discharging, it reflects the change in the lithium ion concentration gradient within the battery's active material; the pure lithium extraction / insertion pressure increment... F li Also known as lithium insertion / extraction expansion force; Additional pressure changes in the battery F extra In addition to the pure lithium insertion / extraction pressure increment during battery charging and discharging processes F li and battery thermal expansion force F thermal Unusual pressure changes are usually caused by side reactions occurring inside the battery, including lithium deposition, lithium stripping, and gas generation. Lithium deposition pressure change F LP The pressure change is defined as the additional pressure increase caused by lithium ion deposition on the negative electrode surface during battery charging, including reversible and irreversible deposition. The pressure changes for reversible and irreversible deposition are respectively defined as reversible deposition pressure changes. F LP,rev and irreversible deposition pressure change F LP,irr ; Pressure change of battery gas production side reaction F gas The pressure change on the outer surface of the battery is defined as the pressure generated by the internal pressure from the decomposition of the SEI film and the reaction of the electrolyte with the active materials. The SEI refers to the solid electrolyte intermediate phase, which is a dynamic interface layer formed by the decomposition of the electrolyte on the electrode surface. Its core function is to inhibit the continuous decomposition of the electrolyte by blocking electron transport and maintaining ion conduction. Lithium stripping pressure change FLS Defined as the pressure change caused by the stripping reaction of active lithium during discharge; S52: Define the formula for the pressure changes caused by each chemical reaction during the charging and discharging process of the battery: S521: The formula for the pressure change caused by each chemical reaction during battery charging is: ; ; ; In formulas (3), (4), and (5): subscripts c Indicates the charging process; F total,c This refers to the change in battery pressure during the charging process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,c The thermal expansion force of the battery during the charging process; F extra,c Additional pressure changes in the battery during the charging process; F LP This represents the change in lithium deposition pressure. F g This represents the pressure change associated with lithium deposition side reactions. F extra,other This indicates an abnormal increase in pressure other than lithium deposition and gas-generating side reactions, including pressure increases caused by SEI film thickening during long-term battery cycling. F LP,rev This represents the change in reversible deposition pressure. F LP,irr This represents the irreversible change in deposition pressure. S522: The formula for the pressure change caused by each chemical reaction during the battery discharge process is: ; ; In equations (6) and (7): subscript d Indicates the discharge process; F total,d This represents the change in battery pressure during the discharge process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,d This refers to the thermal expansion force of the battery during the discharge process. F extra,d Additional pressure changes in the battery during the discharge process; F LS This represents the change in lithium stripping pressure. F extra,otherThis indicates an abnormal increase in pressure other than lithium deposition and gas-generating side reactions, including pressure increases caused by SEI film thickening during long-term battery cycling. S53: Each test consisted of a single low-temperature charge-discharge cycle, and the average rate of change under the characterization conditions was below 0.25C. This suggests that the main side reactions within the battery are lithium deposition and lithium stripping reactions during the charging process. F g , F extra,other The values ​​are all 0. Therefore, the formula for the composition of the chemical reaction pressures during the battery charging and discharging process is: ; ; In equations (8) and (9): subscripts c Indicates the charging process; F total,c This refers to the change in battery pressure during the charging process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,c The thermal expansion force of the battery during the charging process; F LP,rev This represents the change in reversible deposition pressure. F LP,irr This represents the irreversible change in deposition pressure; subscript d Indicates the discharge process; F total,d This represents the change in battery pressure during the discharge process. F thermal,d This refers to the thermal expansion force of the battery during the discharge process. F LS This represents the change in lithium stripping pressure. S54: Based on this, the total battery expansion force, thermal expansion force, and pure lithium insertion / extraction expansion force extracted from S1 to S4 can be used to calculate the expansion force change caused by the additional side reaction of the battery using the formulas (3) to (9). The expansion force change includes the change in lithium deposition pressure. F LP Lithium stripping pressure change F LS and pressure change of lithium deposition side reaction F g .

[0005] Furthermore, the operating ambient temperature of the battery is any value within the range of -10℃ to 50℃, and the charge / discharge rate of the battery is any value within the range of 1 / 5C to 2C.

[0006] Furthermore, the coefficient of thermal expansion of the battery αThe thermal expansion coefficient corresponding to any SOC from 0% to 100% of the battery is used to replace the expansion coefficient curve from 0% to 100% SOC for calculation.

[0007] Furthermore, the coefficient of thermal expansion of the battery α The thermal expansion coefficients at 0% SOC or 100% SOC are used for calculation.

[0008] Furthermore, the battery expansion force-capacity reference curve ensures the absence of battery side reactions through 0.05C charge and discharge data. The change in battery expansion force originates from the insertion and extraction of lithium ions between the positive and negative electrodes, ensuring that the expansion force in the expansion force-capacity reference curve is the pure lithium extraction expansion force.

[0009] Furthermore, the battery side reactions include polarization, lithium plating, and gas production, as well as the temperature rise caused by the polarization, lithium plating, and gas production.

[0010] Furthermore, the additional side reactions of the battery include lithium deposition, lithium stripping, gas generation, and SEI growth, which cause additional expansion force growth in the battery.

[0011] Furthermore, the battery testing platform includes integrated testing fixtures, charging and discharging equipment, and temperature acquisition equipment.

[0012] Furthermore, the integrated testing fixture adopts a constant displacement support mode testing fixture.

[0013] This invention collects electrical, thermal, and mechanical signals of the battery during operation using a battery testing platform. Combining the principles of thermal expansion, the stress-strain constitutive equation of active materials, and Hooke's law, and based on certain assumptions, a decoupling principle for expansion force is established to design a lithium-ion battery expansion force decoupling method. The specific process includes: First, conducting charge-discharge tests at different rates on the battery using the battery testing platform, simultaneously collecting electrical, thermal, and mechanical signals and data from individual battery cells during the charging and discharging process; Second, calculating the battery's thermal expansion force using the battery temperature change curve and thermal expansion coefficient, defining a benchmark expansion force-capacity curve using the expansion force and charging capacity data from low-rate charging tests, and obtaining the lithium insertion / extraction expansion force at different rates through interpolation calculations; Finally, determining the expansion force generated by side reactions such as lithium plating and gas production based on the actual battery operation, thus achieving decoupling of the expansion forces of each chemical reaction.

[0014] The present invention has simple steps, is easy to operate and has high reliability, and is suitable for fault diagnosis and early warning of thermal runaway of power or energy storage batteries based on mechanical performance. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of the lithium-ion battery expansion force decoupling method of the present invention; Figure 2 Temperature rise curves of the battery involved in this invention after charging at different rates at -5°C and discharging at 0.05C; Figure 3 The thermal expansion force curves of the battery involved in this invention after charging at different rates at -5°C and discharging at 0.05C; Figure 4 The lithium insertion / extraction expansion force curves of the battery involved in this invention after charging at different rates at -5°C and discharging at 0.05C; Figure 5 The total expansion force curves of the battery involved in this invention under different charging rates at -5°C; Figure 6 The lithium peeling expansion force curves of the battery involved in this invention after charging at different rates at -5°C and discharging at 0.05C are shown. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings.

[0017] To address the aforementioned problems in the prior art, this invention provides a method for decoupling the expansion force of lithium-ion batteries, such as... Figure 1 As shown, it includes the following steps: S1: Collect battery data and signals, including voltage, current, temperature, temperature rise, and expansion force, through the battery testing platform; S2: Extract temperature and temperature rise data and signals based on the battery data and signals collected in S1, and combine them with the battery thermal expansion coefficient. α Calculating the battery thermal expansion force, which refers to the change in expansion force caused by temperature rise during battery charging and discharging, specifically includes the following steps: S21: In order to accurately calculate the battery thermal expansion force, the thermal expansion coefficient of the battery at different SOCs was tested. Since the thermal expansion coefficients at different SOCs are relatively close, the average value of the thermal expansion coefficients at different SOCs, 0.054kN / ℃, was selected for calculation; SOC refers to the state of charge. S22: This utilizes the battery's thermal expansion force. F thermal Defined as the change in battery pressure caused by changes in battery temperature. F total Due to the influence of the battery's thermal expansion coefficient and state of charge (SOC), the thermal expansion force is positive when the temperature rises and negative when the temperature falls. The calculation formula is as follows: ; (1) In the formula: α The coefficient of thermal expansion of the battery. This refers to the temperature change of the battery during charging and discharging. S23: According to Figure 2The battery temperature rise curve was calculated. Figure 3 Battery thermal expansion force curve; S3: Based on the battery data collected in S1, extract the capacity and expansion force data of the battery at 0.05C charging, and define a battery expansion force-capacity baseline curve to characterize the lithium insertion / extraction expansion force: Define the benchmark interpolation function based on the expansion force curve corresponding to 0.05C: ; In the formula: y i This represents the function value of the expansion force change caused by the lithium insertion / extraction reaction in the battery at a specific capacity. x i Battery charging capacity Q chg or discharge capacity Q dis ; P ( x i () is the interpolation polynomial for the battery charge / discharge capacity; S4: Based on the battery capacity data at charging rates other than 0.05C, and through interpolation calculation using the battery expansion force-capacity baseline curve, this includes calculating the pure lithium insertion / extraction pressure increment during charging and discharging at each charging rate other than 0.05C. F li The curve of change is calculated using the following formula: ; (2) Where: Q chg This refers to the charging capacity. Q dis Discharge capacity; P ( Q chg () is the interpolation polynomial for battery charging capacity; P ( Q dis () is the interpolation polynomial for battery discharge capacity; F li,xC,CC The increment of pure lithium insertion / extraction pressure during charging corresponds to each charging rate other than the 0.05C charging capacity. F li The changing function value; F li,xC,DC The increment of pure lithium insertion / extraction pressure during discharge corresponding to each charging rate other than 0.05C charging capacity. F li The changing function value; S5: Based on the battery expansion force signal and data collected in S1 at any rate, and combined with the battery thermal expansion force and lithium insertion / extraction expansion force calculated in S2, S3, and S4, calculate the expansion force change caused by additional side reactions of the battery, thereby determining the expansion force of the battery in each chemical reaction process, and achieving decoupling of the battery expansion force. Specifically, this includes the following steps: S51: Define the concept of expansion force for each chemical reaction during battery charging and discharging: Battery pressure change F total Defined as the pressure increment during a single charge and discharge cycle of a battery, with a positive value for charging and a negative value for discharging, it reflects the degree of expansion or contraction of the battery's active material particles during the discharge process. Pure lithium insertion / extraction pressure increment F li Defined as the pressure change caused solely by the extraction and insertion of lithium ions within the active material particles during battery charging and discharging, it reflects the change in the lithium ion concentration gradient within the battery's active material; the pure lithium extraction / insertion pressure increment... F li Also known as lithium insertion / extraction expansion force; Additional pressure changes in the battery F extra In addition to the pure lithium insertion / extraction pressure increment during battery charging and discharging processes F li and battery thermal expansion force F thermal Unusual pressure changes are usually caused by side reactions occurring inside the battery, including lithium deposition, lithium stripping, and gas generation. Lithium deposition pressure change F LP The pressure change is defined as the additional pressure increase caused by lithium ion deposition on the negative electrode surface during battery charging, including reversible and irreversible deposition. The pressure changes for reversible and irreversible deposition are respectively defined as reversible deposition pressure changes. F LP,rev and irreversible deposition pressure change F LP,irr ; Pressure change of battery gas production side reaction F gas The pressure change on the outer surface of the battery is defined as the pressure generated by the internal pressure from the decomposition of the SEI film and the reaction of the electrolyte with the active materials. The SEI refers to the solid electrolyte intermediate phase, which is a dynamic interface layer formed by the decomposition of the electrolyte on the electrode surface. Its core function is to inhibit the continuous decomposition of the electrolyte by blocking electron transport and maintaining ion conduction. Lithium stripping pressure change FLS Defined as the pressure change caused by the stripping reaction of active lithium during discharge; S52: Define the formula for the pressure changes caused by each chemical reaction during the charging and discharging process of the battery: S521: The formula for the pressure change caused by each chemical reaction during battery charging is: ; ; ; In formulas (3), (4), and (5): subscripts c Indicates the charging process; F total,c This refers to the change in battery pressure during the charging process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,c The thermal expansion force of the battery during the charging process; F extra,c Additional pressure changes in the battery during the charging process; F LP This represents the change in lithium deposition pressure. F g This represents the pressure change associated with lithium deposition side reactions. F extra,other This indicates an abnormal increase in pressure other than lithium deposition and gas-generating side reactions, including pressure increases caused by SEI film thickening during long-term battery cycling. F LP,rev This represents the change in reversible deposition pressure. F LP,irr This represents the irreversible change in deposition pressure. S522: The formula for the pressure change caused by each chemical reaction during the battery discharge process is: ; ; In equations (6) and (7): subscript d Indicates the discharge process; F total,d This represents the change in battery pressure during the discharge process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,d This refers to the thermal expansion force of the battery during the discharge process. F extra,d Additional pressure changes in the battery during the discharge process; F LS This represents the change in lithium stripping pressure. F extra,otherThis indicates an abnormal increase in pressure other than lithium deposition and gas-generating side reactions, including pressure increases caused by SEI film thickening during long-term battery cycling. S53: Each test consisted of a single low-temperature charge-discharge cycle, and the average rate of change under the characterization conditions was below 0.25C. This suggests that the main side reactions within the battery are lithium deposition and lithium stripping reactions during the charging process. F g , F extra,other The values ​​are all 0. Therefore, the formula for the composition of the chemical reaction pressures during the battery charging and discharging process is: ; ; In equations (8) and (9): subscripts c Indicates the charging process; F total,c This refers to the change in battery pressure during the charging process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,c The thermal expansion force of the battery during the charging process; F LP,rev This represents the change in reversible deposition pressure. F LP,irr This represents the irreversible change in deposition pressure; subscript d Indicates the discharge process; F total,d This represents the change in battery pressure during the discharge process. F thermal,d This refers to the thermal expansion force of the battery during the discharge process. F LS This represents the change in lithium stripping pressure. S54: Based on this, the total battery expansion force, thermal expansion force, and pure lithium insertion / extraction expansion force extracted from S1 to S4 can be used to calculate the expansion force change caused by the additional side reaction of the battery using the formulas (3) to (9). The expansion force change includes the change in lithium deposition pressure. F LP Lithium stripping pressure change F LS and pressure change of lithium deposition side reaction F g .

[0018] Figure 4The figure shows the pure lithium insertion / extraction expansion force curves of the battery after charging at different rates and discharging at 0.05C, calculated in this embodiment. The figure shows that when the voltage is higher than 3.32V, the expansion force is low in sensitivity to the rate, that is, the pure lithium insertion / extraction expansion force corresponding to 0.05C discharge after charging at different rates remains basically unchanged. The fundamental reason is that the expansion or contraction of the battery particles is only related to the degree of lithium insertion or delithiation inside the particles. When the voltage is lower than 3.32V, the polarization difference caused by the difference in charging current causes the battery with a higher rate to reach the cutoff voltage first during discharge, and the expansion force caused by lithium insertion / extraction decreases.

[0019] Optionally, the operating ambient temperature of the battery is any value within the range of -10℃ to 50℃, and the charge / discharge rate of the battery is any value within the range of 1 / 5C to 2C.

[0020] Optionally, the coefficient of thermal expansion of the battery α The thermal expansion coefficient corresponding to any SOC from 0% to 100% of the battery is used to replace the expansion coefficient curve from 0% to 100% SOC for calculation.

[0021] Optionally, the coefficient of thermal expansion of the battery α The thermal expansion coefficients at 0% SOC or 100% SOC are used for calculation.

[0022] Optionally, the battery expansion force-capacity reference curve ensures no battery side reactions through 0.05C charge and discharge data. The change in battery expansion force comes from the insertion and extraction of lithium ions between the positive and negative electrodes, ensuring that the expansion force in the expansion force-capacity reference curve is the pure lithium insertion / extraction expansion force.

[0023] Optionally, the battery side reactions include polarization, lithium plating, and gas production, as well as the temperature rise caused by the polarization, lithium plating, and gas production.

[0024] Optionally, the additional side reactions of the battery include lithium deposition, lithium stripping, gas generation, and SEI growth, which can cause additional expansion force growth in the battery.

[0025] Optionally, the battery testing platform includes an integrated testing fixture, a charging and discharging device, and a temperature acquisition device.

[0026] Optionally, the integrated testing fixture adopts a constant displacement support mode testing fixture.

[0027] In this embodiment, since the battery test environment is -5℃ and it is a single charge-discharge test, based on the aforementioned assumptions, the additional expansion force of the battery under the current test conditions is the lithium deposition expansion force during the charging process. F LP Lithium peeling expansion force during discharge process FLS . Figure 5 The display shows the curve of battery expansion force as a function of battery SOC at different rate of increase, utilizing... Figure 5 By combining the data with step S5, the expansion force caused by additional side reactions in the battery can be decoupled. In this embodiment, it is the lithium deposition expansion force during the charging process. F LP Lithium peeling expansion force during discharge process F LS . Figure 6 The display shows the lithium peeling expansion force of the battery after charging at different rates and discharging at 0.05C. F LS The decoupling results, compared Figure 4 and Figure 6 It can be seen that during battery discharge, when the voltage is higher than 3.32V... F li The difference is small. F LS The difference is significant; the higher the charging rate, F LS The larger the value, the greater the lithium stripping capacity, which indirectly indicates the greater the degree of lithium deposition in the battery. Therefore, the lithium deposition situation of the battery can be characterized by the decoupled lithium stripping expansion force.

[0028] The present invention has simple steps, is easy to operate and has high reliability, and is suitable for fault diagnosis and early warning of thermal runaway of power or energy storage batteries based on mechanical performance.

[0029] The preferred embodiments of the present invention described in detail above with reference to the accompanying drawings are not limited to the specific embodiments described above. Any simple modifications or permutations of the preferred technical solutions described above within the scope of the technical concept of the present invention are all within the protection scope of the present invention.

Claims

1. A method for decoupling the expansion force of a lithium-ion battery, characterized in that: Includes the following steps: S1: Collect battery data and signals, including voltage, current, temperature, temperature rise, and expansion force, through the battery testing platform; S2: Extract temperature and temperature rise data and signals based on the battery data and signals collected in S1, and combine them with the battery thermal expansion coefficient. α Calculating the thermal expansion force of a battery involves the following steps: S21: Test the thermal expansion coefficient of the battery under different SOCs, and select the average value of the thermal expansion coefficient under different SOCs of 0.054kN / ℃ for calculation; S22: This utilizes the battery's thermal expansion force. F thermal Defined as the change in battery pressure caused by changes in battery temperature. F total When the temperature rises, the thermal expansion force is positive; when the temperature falls, the thermal expansion force is negative. The calculation formula is: ; (1) In the formula: α The coefficient of thermal expansion of the battery. This refers to the temperature change of the battery during charging and discharging. S23: Calculate the battery thermal expansion force curve based on the battery temperature rise curve; S3: Based on the battery data collected in S1, extract the capacity and expansion force data of the battery at 0.05C charging, and define a battery expansion force-capacity baseline curve to characterize the lithium insertion / extraction expansion force: Define the benchmark interpolation function based on the expansion force curve corresponding to 0.05C: ; In the formula: y i This represents the function value of the expansion force change caused by the lithium insertion / extraction reaction in the battery at a specific capacity. x i Battery charging capacity Q chg or discharge capacity Q dis ; P ( x i () is the interpolation polynomial for the battery charge / discharge capacity; S4: Based on the battery capacity data at charging rates other than 0.05C, and through interpolation calculation using the battery expansion force-capacity baseline curve, this includes calculating the pure lithium insertion / extraction pressure increment during charging and discharging at each charging rate other than 0.05C. F li The curve of change is calculated using the following formula: ; (2) Where: Q chg This refers to the charging capacity. Q dis Discharge capacity; P ( Q chg () is the interpolation polynomial for battery charging capacity; P ( Q dis () is the interpolation polynomial for battery discharge capacity; F li,xC,CC The increment of pure lithium insertion / extraction pressure during charging corresponds to each charging rate other than the 0.05C charging capacity. F li The changing function value; F li,xC,DC The increment of pure lithium insertion / extraction pressure during discharge corresponding to each charging rate other than 0.05C charging capacity. F li The changing function value; S5: Based on the battery expansion force signal and data collected in S1 at any rate, and combined with the battery thermal expansion force and lithium insertion / extraction expansion force calculated in S2, S3, and S4, calculate the expansion force change caused by additional side reactions of the battery, thereby determining the expansion force of the battery in each chemical reaction process, and achieving decoupling of the battery expansion force. Specifically, this includes the following steps: S51: Define the concept of expansion force for each chemical reaction during battery charging and discharging: Battery pressure change F total Defined as the pressure increment during a single charge and discharge cycle of a battery, with a positive value for charging and a negative value for discharging, it reflects the degree of expansion or contraction of the battery's active material particles during the discharge process. Pure lithium insertion / extraction pressure increment F li Defined as the pressure change caused solely by the extraction and insertion of lithium ions within the active material particles during battery charging and discharging, it reflects the change in the lithium ion concentration gradient within the battery's active material. Additional pressure changes in the battery F extra In addition to the pure lithium insertion / extraction pressure increment during battery charging and discharging processes F li and battery thermal expansion force F thermal Unusual pressure changes are usually caused by side reactions occurring inside the battery, including lithium deposition, lithium stripping, and gas generation. Lithium deposition pressure change F LP The pressure change is defined as the additional pressure increase caused by lithium ion deposition on the negative electrode surface during battery charging, including reversible and irreversible deposition. The pressure changes for reversible and irreversible deposition are respectively defined as reversible deposition pressure changes. F LP,rev and irreversible deposition pressure change F LP,irr ; Pressure change of battery gas production side reaction F gas Defined as the pressure change on the outer surface of the battery caused by the internal pressure generated by the decomposition of the SEI membrane and the reaction of the electrolyte with the active materials; Lithium stripping pressure change F LS Defined as the pressure change caused by the stripping reaction of active lithium during discharge; S52: Define the formula for the pressure changes caused by each chemical reaction during the charging and discharging process of the battery: S521: The formula for the pressure change caused by each chemical reaction during battery charging is: ; ; ; In formulas (3), (4), and (5): subscripts c Indicates the charging process; F total,c This refers to the change in battery pressure during the charging process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,c The thermal expansion force of the battery during the charging process; F extra,c Additional pressure changes in the battery during the charging process; F LP This represents the change in lithium deposition pressure. F g This represents the pressure change associated with lithium deposition side reactions. F extra,other This indicates an abnormal increase in pressure other than lithium deposition and gas-generating side reactions, including pressure increases caused by SEI film thickening during long-term battery cycling. F LP,rev This represents the change in reversible deposition pressure. F LP,irr This represents the irreversible change in deposition pressure. S522: The formula for the pressure change caused by each chemical reaction during the battery discharge process is: ; ; In equations (6) and (7): subscript d Indicates the discharge process; F total,d This represents the change in battery pressure during the discharge process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,d This refers to the thermal expansion force of the battery during the discharge process. F extra,d Additional pressure changes in the battery during the discharge process; F LS This represents the change in lithium stripping pressure. F extra,other This indicates an abnormal increase in pressure other than lithium deposition and gas-generating side reactions, including pressure increases caused by SEI film thickening during long-term battery cycling. S53: Each test consisted of a single low-temperature charge-discharge cycle, and the average rate of change under the characterization conditions was below 0.25C. This suggests that the main side reactions within the battery are lithium deposition and lithium stripping reactions during the charging process. F g , F extra,other The values ​​are all 0. Therefore, the formula for the composition of the chemical reaction pressures during the battery charging and discharging process is: ; ; In equations (8) and (9): subscripts c Indicates the charging process; F total,c This refers to the change in battery pressure during the charging process. F li This is a pure lithium insertion / extraction pressure increment; F thermal,c The thermal expansion force of the battery during the charging process; F LP,rev This represents the change in reversible deposition pressure. F LP,irr This represents the irreversible change in deposition pressure; subscript d Indicates the discharge process; F total,d This represents the change in battery pressure during the discharge process. F thermal,d This refers to the thermal expansion force of the battery during the discharge process. F LS This represents the change in lithium stripping pressure. S54: Based on this, the total battery expansion force, thermal expansion force, and pure lithium insertion / extraction expansion force extracted from S1 to S4 can be used to calculate the expansion force change caused by the additional side reaction of the battery using the formulas (3) to (9). The expansion force change includes the change in lithium deposition pressure. F LP Lithium stripping pressure change F LS and pressure change of lithium deposition side reaction F g .

2. The lithium-ion battery expansion force decoupling method according to claim 1, characterized in that: The operating ambient temperature of the battery is any value within the range of -10℃ to 50℃, and the charge / discharge rate of the battery is any value within the range of 1 / 5C to 2C.

3. The lithium-ion battery expansion force decoupling method according to claim 1, characterized in that: The thermal expansion coefficient of the battery α The thermal expansion coefficient corresponding to any SOC from 0% to 100% of the battery is used to replace the expansion coefficient curve from 0% to 100% SOC for calculation.

4. The lithium-ion battery expansion force decoupling method according to claim 3, characterized in that: The thermal expansion coefficient of the battery α The thermal expansion coefficients at 0% SOC or 100% SOC are used for calculation.

5. The lithium-ion battery expansion force decoupling method according to claim 1, characterized in that: The battery expansion force-capacity reference curve ensures no battery side reactions through 0.05C charge and discharge data. The change in battery expansion force comes from the insertion and extraction of lithium ions between the positive and negative electrodes, ensuring that the expansion force in the expansion force-capacity reference curve is the pure lithium insertion and extraction expansion force.

6. The lithium-ion battery expansion force decoupling method according to claim 5, characterized in that: The battery side reactions include polarization, lithium plating, and gas production, as well as the temperature rise caused by the polarization, lithium plating, and gas production.

7. The lithium-ion battery expansion force decoupling method according to claim 1, characterized in that: The additional side reactions of the battery include lithium deposition, lithium stripping, gas generation, and SEI growth.

8. The lithium-ion battery expansion force decoupling method according to claim 1, characterized in that: The battery testing platform includes integrated testing fixtures, charging and discharging equipment, and temperature acquisition equipment.

9. The lithium-ion battery expansion force decoupling method according to claim 8, characterized in that: The integrated testing fixture adopts a constant displacement support mode testing fixture.

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