A thermal runaway warning device and method for lithium iron phosphate battery

Abstract

A thermal runaway warning device for a lithium iron phosphate battery of the present invention belongs to the field of battery technology, and includes an ultrasonic monitoring component, a stress monitoring component and a host computer; the stress monitoring component includes: a pressure plate, a strain sensor, two clamps, a plurality of fixing bolts and a plurality of sets of nuts; the ultrasonic monitoring component includes: an ultrasonic probe, an aqueous polymer adhesive, an ultrasonic signal generator and a power amplifier. The warning method includes: S1: collecting ultrasonic parameters and stress parameters of the lithium iron phosphate battery; S2: inputting the historical data of the collected ultrasonic parameters and stress parameters into the Kalman filter model to obtain the optimal estimate at the k moment; S3: calculating the comprehensive evaluation parameter J; S4: judging the alarm level according to the comprehensive evaluation parameter. The warning device and method can couple the ultrasonic parameters and stress parameters to automatically judge the thermal runaway warning of the lithium iron phosphate battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a thermal runaway warning device and method for a lithium iron phosphate battery. Background Art

[0002] Lithium iron phosphate batteries are widely used in various electric devices due to their high energy density and safety. However, under extreme conditions, such batteries may still experience thermal runaway, leading to serious safety accidents. Most existing detection technologies use ultrasonic detection or stress parameter monitoring alone, which cannot fully reflect the comprehensive internal and external status of the battery, and the accuracy and timeliness of early warning are low. The reason is that in a complex environment, the change of a single parameter may be interfered by multiple factors, resulting in false alarms or missed alarms. In addition, thermal runaway is the result of the combined action of multiple factors, and single parameter monitoring is difficult to identify the interaction and causal relationship between these complex factors.

[0003] In recent years, the application research of ultrasonic technology and strain sensor technology in battery monitoring has gradually deepened. Ultrasonic technology can provide real-time information on the health status of the internal structure of the battery by detecting cracks and defects inside the battery. Strain sensor technology can reflect the external force and structural strain of the battery by monitoring the stress changes on the outer surface of the battery.

[0004] These two technologies have their own advantages, but it is difficult to fully capture the comprehensive status of the battery when used alone. Therefore, combining ultrasonic detection with strain sensor monitoring to form a multi-parameter coupling analysis method can more accurately reflect the overall health status of the battery and improve the accuracy and timeliness of early warning. Summary of the invention

[0005] A lithium iron phosphate battery thermal runaway early warning device and method of the present invention can provide early warning of a lithium iron phosphate battery thermal runaway based on ultrasonic crack parameter detection and battery outer surface stress parameter coupling.

[0006] In order to achieve the above-mentioned object, a thermal runaway warning device for a lithium iron phosphate battery of the present invention comprises an ultrasonic monitoring component, a stress monitoring component and a host computer;

[0007] The stress monitoring component is used to monitor the stress parameters of lithium iron phosphate batteries, including:

[0008] A pressure-bearing sheet in contact with one side of the lithium iron phosphate battery;

[0009] The strain sensor is bonded to the surface of the pressure-bearing sheet on the side away from the lithium iron phosphate battery and can be electrically connected to the upper machine;

[0010] Two clamps, respectively denoted as clamp A and clamp B, clamp A is located on the side of the lithium iron phosphate battery away from the pressure-bearing sheet, and clamp A abuts against the surface corresponding to the lithium iron phosphate battery; clamp B is located on the side of the strain sensor away from the pressure-bearing sheet, and clamp B abuts against the surface corresponding to the strain sensor;

[0011] A plurality of fixing bolts are passed through the two clamping plates;

[0012] A plurality of sets of nuts are threadedly connected to the fixing bolts, and are used to form a whole with two clamping plates, a plurality of fixing screws, a strain sensor and a pressure-bearing sheet, and the whole abuts against the side of the lithium iron phosphate battery;

[0013] The ultrasonic monitoring component is used to monitor the ultrasonic parameters of lithium iron phosphate batteries, including:

[0014] The ultrasonic probe comprises an ultrasonic transmitting end and an ultrasonic receiving end; the ultrasonic receiving end is electrically connected to the host computer;

[0015] A water-based polymer adhesive is bonded between the ultrasonic transmitting end and the side of the lithium iron phosphate battery;

[0016] An ultrasonic signal generator, used for generating ultrasonic waves;

[0017] The power amplifier is electrically connected to the ultrasonic signal generator and the ultrasonic transmitting end; and can amplify the ultrasonic wave and emit it from the ultrasonic transmitting end.

[0018] Furthermore, the pressure-bearing sheet covers one side surface of the lithium iron phosphate battery, so that once a certain point on the side surface expands, the force will be evenly applied to the pressure-bearing sheet.

[0019] Furthermore, the strain sensor is located in the middle of the pressure-bearing plate, so that when the pressure-bearing plate is subjected to force, the force will be evenly transmitted to the strain sensor.

[0020] Furthermore, the strain sensor is electrically connected to a strain display; and the ultrasonic receiving end is electrically connected to an oscilloscope.

[0021] It can intuitively reflect the stress value and ultrasonic value.

[0022] Furthermore, a thermal runaway warning method for a lithium iron phosphate battery comprises the following steps:

[0023] S1: The host computer continuously and simultaneously collects the ultrasonic parameters and stress parameters of the lithium iron phosphate battery;

[0024] Ultrasonic parameters include: echo amplitude A, echo frequency F and crack length L;

[0025] Stress parameters include: stress value σ and strain value ε;

[0026] S2: input the historical data of ultrasonic parameters and stress parameters collected in S1 into the Kalman filter model, and use the Kalman filter model to obtain the optimal estimate at time k;

[0027] S3: Calculate the comprehensive evaluation parameter J using the optimal estimate of the state at time k in S2;

[0028] S4: Determine the alarm level based on comprehensive evaluation parameters.

[0029] Further, in step S1,

[0030] The calculation formula of echo amplitude A is: A=V max / V ref ; Where V max is the maximum value of the echo signal, V ref is the reference value of the echo signal;

[0031] The calculation formula of echo frequency F is: F = 1 / T; where T is the period of the echo signal;

[0032] The calculation formula of crack length L is: L = V wave / 2f; where V wave is the propagation speed of ultrasound in lithium iron phosphate battery materials; f is the ultrasonic frequency;

[0033] The calculation formula of the stress value σ is: σ=E·ε; where E is the spring modulus of the lithium iron phosphate battery material; ε is the strain value, which is obtained by monitoring the strain sensor.

[0034] Furthermore, the formula of the Kalman filter model is:

[0035]

[0036] In the formula, is the predicted state; is the current state; D is the state transfer matrix, α, β, γ, η, and τ are the coupling coefficients between crack length and stress, ultrasonic echo amplitude and stress, echo frequency and stress, crack length and strain, and ultrasonic echo amplitude and strain, respectively. C and m are material constants; B is the control input matrix,

[0037] S is the cross-sectional area under load, Eκ is the thermal expansion coefficient of the material; the optimal estimate of the state at time k is: Δt is the time interval for collecting data.

[0038] Furthermore, the formula of the comprehensive evaluation parameter J is:

[0039]

[0040] and is the state covariance matrix P k The diagonal elements of have values ​​between 0 and 1.

[0041] Furthermore, the classification criteria for judging the alarm level are:

[0042] If J∈[0,50), it is a first-level warning, i.e., low risk;

[0043] If J∈[50,100), it is a level 2 warning, i.e. medium risk;

[0044] If J∈[100,+∞), it is a level 3 warning, i.e., high risk.

[0045] Beneficial effects:

[0046] The device and method couple the ultrasonic parameters and stress parameters with the Kalman filter model to obtain the optimal estimate of the state at time k, then calculate the comprehensive evaluation parameters based on the estimate, and finally use the values ​​of the comprehensive evaluation parameters to obtain the thermal runaway warning standard, which can realize automatic warning of thermal runaway of lithium iron phosphate batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the overall structure of the early warning device;

[0048] Figure 2 It is a schematic diagram of the positional relationship between the ultrasonic probe, the water-based polymer adhesive and the lithium iron phosphate battery;

[0049] Figure 3 This is a flow chart of the early warning method.

[0050] 1. Pressure plate; 2. Strain sensor; 3. Clamp; 4. Fixing screw; 5. Nut; 6. Strain display; 7. Host computer; 8. Ultrasonic transmitter; 9. Ultrasonic receiver; 10. Water-based polymer adhesive; 12. Ultrasonic signal generator; 13. Power amplifier; 14. Oscilloscope; DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] See Figure 1 and Figure 2 , Embodiment 1: A thermal runaway warning device for a lithium iron phosphate battery, comprising an ultrasonic monitoring component, a stress monitoring component and a host computer 7.

[0053] Ultrasonic monitoring components include:

[0054] The pressure-bearing sheet 1 is made of stainless steel. In this embodiment, the pressure-bearing sheet 1 contacts the side of the lithium iron phosphate battery, and the pressure-bearing sheet 1 covers the entire side of the lithium iron phosphate battery. In this embodiment, the pressure-bearing sheet 1 covers the right side of the lithium iron phosphate battery.

[0055] The strain sensor 2 is a high-precision foil strain gauge, which is bonded to the surface of the pressure-bearing sheet 1 on the side away from the lithium iron phosphate battery. In this embodiment, the strain sensor 2 is located at the center of the pressure-bearing sheet 1 .

[0056] The two clamps 3 are respectively denoted as clamp A and clamp B; wherein clamp A is located on the side of the lithium iron phosphate battery away from the pressure-bearing sheet 1, and clamp A abuts against the surface corresponding to the lithium iron phosphate battery. Clamp B is located on the side of the strain sensor 2 away from the pressure-bearing sheet 1, and clamp B abuts against the surface corresponding to the strain sensor 2.

[0057] Four fixing screws 4 are respectively and simultaneously arranged on the clamping plate A and the clamping plate B. The clamping plate A and the clamping plate B are respectively provided with holes for the fixing bolts to pass through.

[0058] Four sets of nuts 5 are bolted to four fixing screws 4. Each set of nuts 5 includes two nuts 5, which are respectively threaded to the two ends of the corresponding fixing screws 4, and the two nuts 5 are respectively abutted against the corresponding surfaces of the clamping plate A and the clamping plate B. The two sets of nuts 5 are used to form a whole with the two clamping plates 3, the two fixing screws 4, the strain sensor 2 and the pressure plate 1, and the whole abuts against the side of the lithium iron phosphate battery. It is used to more accurately reflect the stress changes of the lithium iron phosphate battery.

[0059] The strain display 6 is electrically connected to the strain sensor 2 and can display the stress data monitored by the strain sensor 2. The host computer 7 is electrically connected to the strain display 6 and can analyze the collected stress data.

[0060] See Figure 2 , ultrasonic monitoring components include:

[0061] The ultrasonic probe comprises an ultrasonic transmitting end 8 and an ultrasonic receiving end 9.

[0062] The water-based polymer adhesive 10 is bonded between the ultrasonic emitting end 8 and the upper surface of the lithium iron phosphate battery in this embodiment. The water-based polymer adhesive 10 acts as an ultrasonic coupling agent to eliminate the interference of impurities between the ultrasonic emitting end 8 and the upper surface of the lithium iron phosphate battery.

[0063] The ultrasonic signal generator 12 is used to generate ultrasonic waves and adopts a highly sensitive piezoelectric ultrasonic generator.

[0064] The power amplifier 13 is electrically connected to the ultrasonic signal generator 12 and is also electrically connected to the ultrasonic transmitting end 8. The power amplifier 13 can amplify the ultrasonic wave generated by the ultrasonic signal generator 12, and the amplified ultrasonic wave signal is emitted from the ultrasonic transmitting end 8.

[0065] The oscilloscope 14 is electrically connected to the ultrasonic receiving terminal 9 and is used to display the ultrasonic wave. The host computer 7 is electrically connected to the oscilloscope 14 and is used to receive and analyze the ultrasonic wave information.

[0066] Example 2: See Figure 3 , a lithium iron phosphate battery thermal runaway early warning method, comprising the following steps:

[0067] S1: The host computer continuously and simultaneously collects the ultrasonic parameters and stress parameters of the lithium iron phosphate battery.

[0068] The principle of ultrasonic testing is based on the propagation characteristics of sound waves in different materials. By monitoring the changes in the echo signal, internal cracks or defects can be identified.

[0069] The strain sensor calculates the stress value by measuring the tiny deformation of the material under stress. It has high sensitivity and accuracy and can reflect the external force conditions of the battery in real time.

[0070] Ultrasonic parameters include:

[0071] The echo amplitude A is obtained by calculating the ratio of the maximum value of the echo signal to the reference value. The calculation formula is:

[0072] A=V max / V ref ;

[0073] Where V max is the maximum value of the echo signal, which is obtained by monitoring the ultrasonic receiving end; V ref is the reference value of the echo signal, a known value.

[0074] Echo frequency F: obtained by calculating the period of the echo signal. The calculation formula is:

[0075] F = 1 / T;

[0076] Where T is the period of the echo signal, which is monitored by the ultrasonic receiving end.

[0077] Crack length L: obtained by the propagation speed and frequency of ultrasonic waves in the material. The calculation formula is:

[0078] L=Vwave / 2f

[0079] Where V wave is the propagation speed of ultrasound in lithium iron phosphate battery materials; f is the ultrasonic frequency.

[0080] Stress parameters include:

[0081] The relationship between stress and strain. The stress parameter is measured by the strain sensor directly to measure the strain value, and then converted into the stress value through the elastic modulus of the material. The formula is:

[0082] σ=E·ε

[0083] Where, E is the spring modulus of the lithium iron phosphate battery material; ε is the strain value, which is obtained by monitoring the strain sensor; σ is the stress value.

[0084] S2: The historical data of ultrasonic parameters and stress parameters collected in S1 are input into the Kalman filter model, and the Kalman filter model is used to obtain the optimal estimate at time k.

[0085] Specifically, the Kalman filter equation is:

[0086]

[0087] In the formula, is the predicted state, that is, the predicted state at time k;

[0088] is the current state; that is, the state at time k-1;

[0089] D is the state transfer matrix; it describes how the system state transfers from one time step to the next time step. The state transfer matrix coefficients can be obtained through the dynamic equations established by material mechanics and ultrasonic propagation theory.

[0090] B is the control input matrix, u k-1 is the control input. The control input matrix describes how the control input affects the system state. In the lithium battery thermal runaway warning, the control input includes the external force and the effect of temperature change on stress.

[0091] In formula (1),

[0092]

[0093]

[0094] Among them, α, β, γ, η, and τ are the coupling coefficients of crack length and stress, ultrasonic echo amplitude and stress, echo frequency and stress, crack length and strain, and ultrasonic echo amplitude and strain, respectively, and Δt is the time interval for collecting data.

[0095] S is the cross-sectional area under load, and Eκ is the thermal expansion coefficient of the material. In addition, Here, C and m are material constants.

[0096] Error covariance update equation:

[0097] P kk =(IK k H)P kk-1 (4)

[0098] I is the identity matrix. K k is the Kalman gain; H is the observation matrix; P kk-1 is the prediction error covariance; P kk Forecast error covariance update;

[0099] Kalman gain:

[0100] K k =P kk-1 H T (HP kk-1 H T +R) -1 (3)

[0101] P kk-1 is the prediction error covariance, R is the measurement noise covariance; H T Represents the transpose of the observation matrix.

[0102] The update equation is:

[0103]

[0104] in, is the updated state, K k is the Kalman gain, Z k is the actual measurement value, H is the observation matrix; the actual measurement value includes the ultrasonic parameters collected by the ultrasonic sensor and the stress parameters collected by the stress sensor. Through these real-time data, the predicted state is corrected to obtain a more accurate current state estimate.

[0105] The state variables in the Kalman filter, such as crack length, ultrasonic echo amplitude, ultrasonic echo frequency, and strain, provide key information about the dynamic state of the system. Through the prediction and update phases, the Kalman filter can continuously correct the estimated values ​​of these state variables, thereby providing the optimal estimate of the system at time k, that is,

[0106]

[0107] S3: Use the optimal estimate of the state at time k in S2 to calculate the comprehensive evaluation parameters.

[0108] The calculation formula of comprehensive evaluation parameters is:

[0109]

[0110] and is the state covariance matrix P k The diagonal elements of are all between 0 and 1. The comprehensive evaluation parameter J is used to evaluate the thermal runaway risk of the battery. At the initial moment of the Kalman filter k = 0, the initial state covariance matrix P0 needs to be given. If the uncertainty of the initial state estimate is large, a larger initial covariance can be set; otherwise, a smaller initial covariance is set.

[0111] S4: Determine the alarm level based on comprehensive evaluation parameters.

[0112] The criteria for judgment are:

[0113] If J∈[0,50), it is a first-level warning, i.e., low risk; the system prompts to conduct routine inspection and monitoring;

[0114] If J∈[50,100), it is a level 2 warning, i.e. medium risk; the system prompts to take certain preventive measures, such as cooling or reducing load;

[0115] If J∈[100,+∞), it is a level 3 warning, i.e. high risk. The system prompts you to stop using the battery immediately and replace or repair it.

[0116] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A thermal runaway warning device for a lithium iron phosphate battery, characterized in that: It includes an ultrasonic monitoring component, a stress monitoring component and a host computer (7); The stress monitoring component is used to monitor the stress parameters of lithium iron phosphate batteries, including: A pressure-bearing sheet (1) in contact with one side surface of the lithium iron phosphate battery; The strain sensor (2) is bonded to a surface of the pressure-bearing sheet (1) on a side away from the lithium iron phosphate battery and can be electrically connected to the host computer (7); Two clamping plates (3), respectively denoted as clamping plate A and clamping plate B, clamping plate A is located on the side of the lithium iron phosphate battery away from the pressure-bearing plate (1), and clamping plate A abuts against the surface corresponding to the lithium iron phosphate battery; clamping plate B is located on the side of the strain sensor (2) away from the pressure-bearing plate (1), and clamping plate B abuts against the surface corresponding to the strain sensor (2); A plurality of fixing bolts are passed through the two clamping plates (3); A plurality of sets of nuts (5) are threadedly connected to the fixing bolts and are used to form a whole with two clamping plates (3), a plurality of fixing screws (4), a strain sensor (2) and a pressure-bearing sheet (1), and the whole abuts against the side of the lithium iron phosphate battery; The ultrasonic monitoring component is used to monitor the ultrasonic parameters of lithium iron phosphate batteries, including: The ultrasonic probe comprises an ultrasonic transmitting end (8) and an ultrasonic receiving end (9); the ultrasonic receiving end (9) is electrically connected to the host computer (7); A water-based polymer adhesive (10) is bonded between the ultrasonic transmitting end (8) and the side surface of the lithium iron phosphate battery; An ultrasonic signal generator (12), used for generating ultrasonic waves; A power amplifier (13) is electrically connected to the ultrasonic signal generator (12) and the ultrasonic transmitting end (8); and is capable of amplifying ultrasonic waves and transmitting the ultrasonic waves from the ultrasonic transmitting end (8); A warning method based on a thermal runaway warning device for a lithium iron phosphate battery comprises the following steps: S1: The host computer continuously and simultaneously collects the ultrasonic parameters and stress parameters of the lithium iron phosphate battery; Ultrasonic parameters include: echo amplitude A, echo frequency F and crack length L; Stress parameters include: stress value s and strain value ε; S2: input the historical data of ultrasonic parameters and stress parameters collected in S1 into the Kalman filter model, and use the Kalman filter model to obtain the optimal estimate at time k; S3: Calculate the comprehensive evaluation parameter J using the optimal estimate of the state at time k in S2; S4: Determine the alarm level based on comprehensive evaluation parameters.

2. A thermal runaway warning device for a lithium iron phosphate battery according to claim 1, characterized in that: The pressure-bearing sheet (1) covers one side surface of the lithium iron phosphate battery.

3. A thermal runaway warning device for a lithium iron phosphate battery according to claim 2, characterized in that: The strain sensor (2) is located in the middle of the pressure-bearing sheet (1).

4. A thermal runaway warning device for a lithium iron phosphate battery according to claim 1, characterized in that: The strain sensor (2) is electrically connected to a strain display (6); and the ultrasonic receiving end (9) is electrically connected to an oscilloscope (14).

5. A thermal runaway warning device for a lithium iron phosphate battery according to claim 1, characterized in that: In step S1, The calculation formula of echo amplitude A is: A=V max / V ref ; Where V max is the maximum value of the echo signal, V ref is the reference value of the echo signal; The calculation formula of echo frequency F is: F = 1 / T; where T is the period of the echo signal; The calculation formula of crack length L is: L = V wave / 2f; where V wave is the propagation speed of ultrasound in lithium iron phosphate battery materials; f is the ultrasonic frequency; The calculation formula of the stress value s is: s=E×ε; where E is the spring modulus of the lithium iron phosphate battery material; ε is the strain value, which is obtained by monitoring the strain sensor.

6. A thermal runaway warning device for a lithium iron phosphate battery according to claim 5, characterized in that: In step S2: the formula of the Kalman filter model is: In the formula, is the predicted state; is the current state; D is the state transfer matrix, u k-1 is the control input; α, b, γ, h, and t are the coupling coefficients between crack length and stress, ultrasonic echo amplitude and stress, echo frequency and stress, crack length and strain, and ultrasonic echo amplitude and strain, respectively. C and m are material constants; B is the control input matrix, S is the cross-sectional area under load, Ek is the thermal expansion coefficient of the material; the optimal estimate of the state at time k is: Δt is the time interval for collecting data.

7. A thermal runaway warning device for a lithium iron phosphate battery according to claim 6, characterized in that: In step S3, the formula of the comprehensive evaluation parameter J is: and is the state covariance matrix P k The diagonal elements of have values ​​between 0 and 1.

8. A thermal runaway warning device for a lithium iron phosphate battery according to claim 7, characterized in that: The criteria for judging the alarm level are: If J∈[0,50), it is a first-level warning, i.e., low risk; If J∈[50,100), it is a level 2 warning, i.e. medium risk; If J∈[100,+￥), it is a level 3 warning, i.e., high risk.

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