Strain and temperature parameter coupled lithium iron phosphate energy storage battery thermal runaway grading early warning method

Abstract

The invention relates to a strain and temperature parameter coupled lithium iron phosphate energy storage battery thermal runaway grading early warning method, and belongs to the technical field of lithium iron phosphate energy storage battery thermal runaway early warning methods, and the method comprises the following steps: S1, building a temperature change model of lithium iron phosphate energy storage battery thermal runaway; s2, establishing a gas volume expansion model of thermal runaway of the lithium iron phosphate energy storage battery; s3, establishing a thermal runaway shell strain model of the lithium iron phosphate energy storage battery; s4, establishing a temperature and strain coupling model of thermal runaway of the lithium iron phosphate energy storage battery; and S5, based on the coupling model between the temperature and the strain in the thermal runaway process of the battery, setting a grading early warning threshold value. According to the method, accurate description and quantitative evaluation of the thermal runaway process are realized by integrating multi-dimensional data of temperature-strain. An early warning threshold system based on a coupling mechanism is constructed, the false alarm rate and the missing report rate can be reduced, key features of the thermal runaway process can be captured, and a safety response whole-process dynamic early warning system is formed.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal runaway early warning methods for lithium iron phosphate energy storage batteries, and particularly relates to a thermal runaway grading early warning method for lithium iron phosphate energy storage batteries that couples strain and temperature parameters. Background Technique

[0002] Lithium iron phosphate energy storage batteries may undergo thermal runaway under extreme conditions such as overcharging, over-discharging, high temperature, or short circuit, resulting in a sharp rise in internal temperature, rapid generation and release of gas, and significant stress and strain changes on the outer shell. These processes seriously threaten the safety of the battery system.

[0003] Digital Image Correlation (DIC) can accurately monitor the micro-strain on the battery surface; an infrared thermal imager can monitor the surface temperature in real time. Although DIC and infrared thermal imagers are commonly used to obtain strain and temperature data in the thermal runaway early warning of lithium iron phosphate energy storage batteries, in existing thermal runaway early warning methods, they mainly rely on single-parameter monitoring, without constructing an early warning mechanism based on the coupling of strain and temperature, and cannot perform multi-parameter collaborative analysis.

[0004] In actual situations, the thermal runaway process of lithium iron phosphate energy storage batteries is the result of complex interactions between multiple physical fields such as temperature, stress, strain, and gas expansion. The decomposition reaction of internal materials under high temperature generates gas, and the gas expansion exerts pressure on the outer shell, resulting in stress changes and manifested as an increase in surface strain. The increase in temperature not only accelerates the reaction rate but also changes the mechanical properties of the outer shell material, such as the elastic modulus and thermal expansion coefficient, making the coupling relationship between strain and temperature more complex and dynamic.

[0005] The above existing early warning methods can only perform single-parameter monitoring, with limitations such as response lag, single data, and high false alarm rate, and it is difficult to comprehensively and accurately reflect the complex multi-physical field evolution process of thermal runaway. Therefore, it is necessary to construct a strain and temperature coupling model by integrating multi-dimensional data of temperature-strain to achieve an accurate description and quantitative evaluation of the thermal runaway process. Summary of the Invention

[0006] A thermal runaway grading early warning method for lithium iron phosphate energy storage batteries that couples strain and temperature parameters of the present invention constructs a coupling model of strain and temperature to achieve an accurate description and quantitative evaluation of the thermal runaway of lithium iron phosphate energy storage batteries.

[0007] A thermal runaway grading early warning method for lithium iron phosphate energy storage batteries that couples strain and temperature parameters of the present invention includes the following steps: S1: Establish a temperature change model for the thermal runaway of lithium iron phosphate energy storage batteries; S2: Establish a gas volume expansion model for the thermal runaway of lithium iron phosphate energy storage batteries; S3: Establish a shell strain model for the thermal runaway of lithium iron phosphate energy storage batteries; S4: Establish a coupling model of temperature and strain for the thermal runaway of lithium iron phosphate energy storage batteries; S5: Based on the coupling model between temperature and strain during the thermal runaway of the battery, set hierarchical warning thresholds.

[0008] Further, step S1 includes the following steps: S1.1: Establish the temperature T ( t ) within the battery, and the balance equations for heat generation and heat dissipation:

[0009] Among them, C cell is the total heat capacity of the battery; Q gen ( t ) is the total heat generation per unit time of the battery; Q loss ( t ) is the total heat dissipation per unit time of the battery; S1.2: Establish an equation for the total heat generation per unit time of the battery:

[0010] Among them, I short is the internal short-circuit current of the battery; R short is the internal short-circuit resistance of the battery; Q short ( t ) is the heat generation from the internal short-circuit reaction of the battery; Q gas ( t ) is the heat of gas generation reaction of the battery;

[0011] Among them, n i ( t ) is the molar amount of the i th gas generated; is the enthalpy change of formation of the reaction corresponding to the i th gas; S1.3: Establish an equation for the total heat dissipation per unit time:

[0012] Among them, h is the heat transfer coefficient on the outer surface of the battery; A cellis the external surface area of the battery; T ( t ) is the temperature inside the battery; T env is the ambient temperature.

[0013] Furthermore, step S2 includes the following steps: S2.1: Establish the expansion volume of the gas V g ( t ) , the equation affected by temperature and gas type:

[0014] where, n i ( t ) is the molar amount of the i th gas generated; R is the ideal gas constant; T ( t ) is the temperature inside the battery; P g ( t ) is the internal pressure of the battery; S2.2: Describe the gas generation rate with the Arrhenius formula:

[0015] where, k i is the reaction rate constant of the i th gas, E i is the reaction activation energy of the i th gas, C i ( t ) is the concentration of the gas generation reactant of the i th gas.

[0016] Furthermore, step S3 includes the following steps: S3.1: Battery housing strain The equation with thermal expansion strain and mechanical strain:

[0017] S3.2: Describe the thermal expansion strain with temperature change, the formula is:

[0018] where, a is the thermal expansion coefficient of the battery housing material, T 0 is the initial temperature; S3.3: Describe mechanical strain using gas expansion, with the formula:

[0019] where P g ( t ) is the internal pressure of the battery; t wall is the thickness of the battery casing; E is the elastic modulus of the battery casing material; R cell is the geometric characteristic dimension of the battery casing; The internal pressure of the battery is expressed as:

[0020] where n i ( t ) is the molar amount of the i th gas generated, R is the ideal gas constant, T ( t ) is the internal temperature of the battery; V g (t) is the sum of the volumes of all gases, V cell is the volume of the battery.

[0021] Furthermore, step S4 includes: S4.1: The strain model is:

[0022] S4.2: The temperature model is:

[0023] S4.3: Simultaneously solve equations (12) and (13) to establish a coupling model between temperature and strain during the thermal runaway process of the battery.

[0024] Furthermore, the hierarchical warning threshold is set as: I. Normal, no warning; When the strain change rate is less than or equal to 1 times the temperature change rate, i.e., , the system has no warning; II. Level 1, slightly abnormal; When the change rate of strain is greater than 1 times and less than or equal to 5 times the temperature change rate, i.e., , the system determines it as Level 1 and gives a corresponding alarm to remind personnel to check the battery;

[0025] III. Level 2, moderately abnormal; When the change rate of strain is greater than 5 times and less than or equal to 10 times the change rate of temperature, that is, the system determines it as level 2, and the system starts the cooling system to cool the battery; IV. Level 3, serious abnormality; When the change rate of strain is greater than 10 times the change rate of temperature, that is, the system determines it as level 3, and the system starts emergency power-off and fire extinguishing measures.

[0026] Beneficial effects: By comprehensively analyzing multi-dimensional data of temperature-strain, this method realizes the accurate description and quantitative evaluation of the thermal runaway process. Constructing an early warning threshold system based on the coupling mechanism can not only significantly reduce the false alarm rate and missed alarm rate, but also capture the key characteristics of the thermal runaway process, forming a full-process dynamic early warning system from early risk warning to emergency safety response, providing technical support for improving the safety of energy storage batteries. Through multi-parameter collaborative analysis, the coupling early warning method of strain and temperature can achieve refined hierarchical management, promoting the development of energy storage battery monitoring technology towards intelligence and precision. Description of the drawings

[0027] Figure 1 It is a schematic diagram of the results of the theoretical model and experimental values of the coupling relationship between temperature and strain. Specific implementation manners

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] A method for thermal runaway hierarchical early warning of lithium iron phosphate energy storage batteries with coupled strain and temperature parameters includes the following steps: S1: Establish a temperature change model for the thermal runaway of lithium iron phosphate energy storage batteries; Establish the temperature T ( t ) inside the battery, the balance equation of the heat source (heat generation) and heat dissipation, expressed as:

[0030] Wherein, C cell is the total heat capacity of the battery; Q gen ( t ) is the total heat generation per unit time of the battery;Q loss ( t ) is the total heat dissipation of the battery per unit time.

[0031] The total heat generation of the battery per unit time Q gen ( t ) also includes the heat generation from internal short - circuit reaction and the heat of gas - generating reaction, expressed as:

[0032] Among them, I short is the internal short - circuit current of the battery; R short is the internal short - circuit resistance of the battery; Q short ( t ) is the heat generation from the internal short - circuit reaction of the battery; Q gas ( t ) is the heat of gas - generating reaction of the battery.

[0033] Among them, Q gas ( t ) is expressed as:

[0034] Among them, n i ( t ) is the molar amount of the i th gas generated; is the enthalpy change of formation of the reaction corresponding to the i th gas; Heat dissipation Q loss ( t ) is determined by the heat transfer from the outer surface of the battery:

[0035] Among them, h is the heat transfer coefficient of the outer surface of the battery; A cell is the outer surface area of the battery; T ( t ) is the temperature inside the battery; T env is the ambient temperature.

[0036] S2: Establish a gas volume expansion model for the thermal runaway of lithium iron phosphate energy storage batteries; The expansion volume of the gas V g ( t) is the sum of the volumes of all different types of gases, affected by temperature and gas type, expressed as:

[0037] Among them, n i ( t ) is the molar amount of the i th type of gas generated; R is the ideal gas constant; T ( t ) is the temperature inside the battery; P g ( t ) is the internal pressure of the battery.

[0038] The gas generation rate is described by the Arrhenius equation:

[0039] Among them, k i is the reaction rate constant of the i th type of gas, E i is the reaction activation energy of the i th type of gas, C i ( t ) is the concentration of the gas generation reactant of the i th type of gas.

[0040] S3: Establish a shell strain model for the thermal runaway of lithium iron phosphate energy storage batteries; The shell strain of the battery includes the following two parts, the thermal expansion strain caused by temperature and the mechanical strain caused by internal gas expansion; expressed as:

[0041] Among them, the thermal expansion strain is related to the temperature change, expressed as:

[0042] Among them, a is the thermal expansion coefficient of the battery shell material, T 0 is the initial temperature.

[0043] The mechanical strain is caused by gas expansion, expressed as:

[0044] Among them, P g ( t ) is the internal pressure of the battery;t wall is the battery casing thickness; E is the elastic modulus of the battery casing material; R cell is the geometric characteristic size of the battery casing; The internal pressure of the battery is expressed as:

[0045] in, n i ( t ) is the i The molar amount of gas produced, R is the ideal gas constant, T ( t ) is the temperature inside the battery; V g (t) is the sum of the volumes of all gases, V cell is the volume of the battery; S4: Establish a coupled model of temperature and strain for thermal runaway of lithium iron phosphate energy storage batteries;

[0046] temperature T ( t ) is described by the following differential equation:

[0047] By combining equations (12) and (13), a coupling model between temperature and strain during battery thermal runaway is established.

[0048] S5: Based on the coupling model between temperature and strain during battery thermal runaway, set the graded warning threshold.

[0049] Setting of graded warning thresholds: 1. Normal without warning; When the strain change rate is less than or equal to 1 times the temperature change rate, that is, There is no system warning.

[0050] At this time, it indicates that the battery is in normal working condition, the temperature is low, the strain change is slight, and the system has no warning response.

[0051] 2. Level 1, slight abnormality; When the rate of change of strain is greater than 1 times and less than or equal to 5 times the rate of change of temperature, that is, When the system determines it as level 1, it will issue a corresponding alarm; At this time, the temperature begins to rise, and the gas expansion effect begins to appear, but the change in strain is small. Remind the operator to pay attention to the temperature change of the battery.

[0052] III. Level 2, moderate anomaly; When the change rate of strain is greater than 5 times and less than or equal to 10 times the change rate of temperature, that is, The system determines it as Level 2 and activates the cooling system to cool the battery; at this time, both the temperature and strain have risen significantly, and the strain and gas expansion effect are more obvious.

[0053] IV. Level 3, severe anomaly.

[0054] When the change rate of strain is greater than 10 times the change rate of temperature, At this time; the system determines it as Level 3 and activates emergency power-off and fire extinguishing measures.

[0055] At this time, the battery temperature and strain have reached a very high level, indicating that the battery has approached or entered the thermal runaway stage, and the pressure effect of gas expansion on the battery shell has been significant. Immediately trigger safety measures such as emergency power-off and fire extinguishing.

[0056] Application example Suppose that during the actual use of a lithium iron phosphate battery, the thermal expansion coefficient: the thermal expansion coefficient of the battery shell material is 23.2×10 -6 / °C; the internal short-circuit resistance and internal short-circuit current are 0.001 Ω and 3400 A respectively; the square shell size: the size common to 314 Ah batteries is: 175 mm×205 mm×70 mm; the initial pressure and initial temperature are 101325 Pa and 25 o °C.

[0057] Use the digital image method technology DIC to obtain the distribution and dynamic change of the strain on the battery surface; use an infrared thermal imager to monitor the temperature of the battery surface.

[0058] Adopt the numerical method for discretization, the finite difference method. For the temperature equation in Equation (12), it is discretized as:

[0059] For the strain equation, directly use the current temperature T(t) to calculate the strain:

[0060] Based on MATLAB, through the iterative calculation of Equation (14) and Equation (15); calculate the coupling relationship diagram of temperature and strain during the thermal runaway process, as Figure 1As shown, the experimental curve under the same boundary has a high degree of coincidence with the theoretical value under this working condition. This figure shows the theoretical calculation curves of temperature and strain obtained by calculating according to the coupling equations (14) and (15) under the condition that the linear expansion coefficient generated by the material due to temperature change is 23.2×10 -6 / ℃; the internal short-circuit resistance and internal short-circuit current are 0.001Ω and 3400A respectively; the size of the square shell is 175mm×205mm×70mm common to 314Ah batteries; the initial pressure and temperature are 101325Pa and 25 o °C respectively, as well as the experimental values under the same boundary conditions.

[0061] When the battery temperature change rate rises to 1°C / s and the strain change rate is 3 / s, at this time, temperature is used as the main criterion, and the system determines it as level 1 and issues a warning.

[0062] When the temperature change rate becomes 0.2°C / s and the strain change rate is 1.9 / s, the system determines it as level 2, and the system starts the cooling system.

[0063] When the temperature change rate is 0.1°C / s and the strain change rate is 2 / s, the system determines it as level 3, and the system immediately starts emergency power-off and fire extinguishing measures to ensure safety. The system of this solution is a battery management system.

[0064] Inspired by the above ideal embodiments of the present invention, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A thermal runaway hierarchical warning method for lithium iron phosphate energy storage batteries coupled with strain and temperature parameters, characterized in that: The following steps are involved: S1: Establish a temperature change model for thermal runaway of lithium iron phosphate energy storage batteries; S2: Establish a gas volume expansion model for thermal runaway of lithium iron phosphate energy storage batteries; S3: Establish a shell strain model for thermal runaway of lithium iron phosphate energy storage batteries; S4: Establish a coupled model of temperature and strain for thermal runaway of lithium iron phosphate energy storage batteries; S5: Based on the coupling model between temperature and strain during battery thermal runaway, set the graded warning threshold.

2. According to claim 1, a thermal runaway graded warning method for lithium iron phosphate energy storage battery coupled with strain and temperature parameters is characterized in that: Step S1 includes the following steps: S1.1: Establishing the temperature inside the battery T ( t ), the balance equation of heat generation and heat loss: ； in, C cell is the total heat capacity of the battery; Q gen ( t ) is the total heat generated by the battery per unit time; Q loss ( t ) is the total heat dissipation of the battery per unit time; S1.2: Establish the equation for the total heat generated by the battery per unit time: ； in, I short It is the short-circuit current in the battery; R short is the short-circuit resistance inside the battery; Q short ( t ) is the heat generated by the short-circuit reaction in the battery; Q gas ( t ) is the heat of gas generation reaction of the battery; ； in, n i ( t ) is the i The molar amount of the gas produced; It is i The enthalpy change of the reaction corresponding to the gas; S1.3: Develop an equation for the total heat dissipation per unit time: ； in, h is the heat transfer coefficient of the battery's outer surface; A cell is the battery surface area; T ( t ) is the temperature inside the battery; T env is the ambient temperature.

3. According to claim 2, a thermal runaway hierarchical early warning method for lithium iron phosphate energy storage batteries coupled with strain and temperature parameters is characterized in that: Step S2 includes the following steps: S2.1: Establishing the expanded volume of the gas V g ( t ), affected by temperature and gas type equation: ； in, n i ( t ) is the i The molar amount of the gas produced; R is the ideal gas constant; T ( t ) is the temperature inside the battery; P g ( t ) is the internal pressure of the battery; S2.2: Use the Arrhenius formula to describe the gas production rate: ； in, k i It is i The reaction rate constant of the gas, E i It is i The activation energy of the gas reaction, C i ( t ) is the i The concentration of the gas-producing reactant in a gas.

4. According to claim 3, a thermal runaway graded warning method for lithium iron phosphate energy storage battery coupled with strain and temperature parameters is characterized in that: Step S3 includes the following steps: S3.1: Battery Enclosure Strain Equations for thermal expansion strain and mechanical strain: ； S3.2: Thermal expansion strain is described by temperature change using the formula: ； in, a is the thermal expansion coefficient of the battery casing material, T 0 is the initial battery temperature; S3.3: Mechanical strain is described by gas expansion using the formula: ； in, P g ( t ) is the internal pressure of the battery; t wall is the battery casing thickness; E is the elastic modulus of the battery casing material; R cell is the geometric characteristic dimension of the battery shell; the internal pressure of the battery is expressed as: ； in, n i ( t ) is the i The molar amount of gas produced, R is the ideal gas constant, T ( t ) is the temperature inside the battery; V g (t) is the sum of the volumes of all gases, V cell is the volume of the battery.

5. The method for thermal runaway graded warning of lithium iron phosphate energy storage battery coupled with strain and temperature parameters according to claim 4 is characterized in that: Step S4 includes: S4.1: The strain model is: ； S4.2: The temperature model is: ； S4.3: Combine equations (12) and (13) to establish a coupling model between temperature and strain during battery thermal runaway.

6. The method for thermal runaway graded early warning of lithium iron phosphate energy storage battery coupled with strain and temperature parameters according to claim 5 is characterized in that: In step S5, the hierarchical warning threshold is set as:

1. Normal, no warning; When the strain change rate is less than or equal to 1 times the temperature change rate, that is, When the system has no warning; 2. Level 1, slight abnormality; When the rate of change of strain is greater than 1 times and less than or equal to 5 times the rate of change of temperature, that is, When the system determines it as level 1, it will issue a corresponding alarm to remind personnel to check the battery; 3. Level 2, moderate abnormality; When the rate of change of strain is greater than 5 times and less than or equal to 10 times the rate of change of temperature, that is, When the system determines it as level 2, the system starts the cooling system to cool the battery; 4. Level 3, severe abnormality; When the rate of change of strain is greater than 10 times the rate of change of temperature, that is, When the system is judged as level 3, the system initiates emergency power off and fire extinguishing measures.

Images