Early warning method and system for initial pressure relief of lithium battery thermal runaway

Abstract

The invention provides an early warning method and system for initial pressure relief of lithium battery thermal runaway. The method comprises the following steps: S1, acquiring the pressure and temperature of gas in a battery pack; s2, calculating the amount of a gas substance by using a Van der Waals equation; s3, calculating the increment of the amount of the gas substance within the set time; s4, judging whether the increment is greater than an increment threshold or not, and if so, determining that initial thermal runaway occurs; if not, returning to S1; according to the method, on the premise that the thermal runaway early warning function is achieved, complex sensing equipment is not additionally arranged, the Van der Waals equation conforming to the actual gas state is adopted for calculating the gas amount in the battery pack, and the forecasting accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery thermal runaway detection, and in particular to an early warning method and system for pressure release in the early stage of thermal runaway of a lithium battery. Background Art

[0002] With the development of lithium-ion batteries in new energy vehicles and the rise of electrochemical energy storage applications, the advantages of lithium batteries such as high energy density, long service life, low self-discharge rate, flexible layout and no memory effect have gradually become well known to people. At the same time, the safe use of lithium batteries has also attracted more and more attention. Before a lithium battery safety accident occurs, it will experience thermal runaway. In the thermal runaway state, a large amount of gas is generated inside the battery, causing the internal pressure of the battery to increase sharply, causing the safety valve of cylindrical batteries or square aluminum shell batteries to open and the edge of the soft-pack battery to crack, etc. These situations will cause a large amount of internal gas to overflow. At this time, if an early warning can be issued in time and measures such as power off and cooling can be taken, the occurrence of safety accidents can be avoided or slowed down, thereby protecting the lives of people and reducing property losses; if an early warning is not issued in time and the battery continues to be used, it is very easy to cause combustion or even explosion accidents. Therefore, the monitoring of lithium battery safety valves and edge sealing status has attracted more and more attention from BMS developers. It is of great significance for early warning of lithium battery thermal runaway and ensuring the safety of battery use. At present, the monitoring of battery thermal runaway is mainly through temperature monitoring, combustible gas detection and other methods. The temperature monitoring method alone cannot provide early warning when the temperature has not risen significantly in the early stage of thermal runaway. In addition, the battery itself is at a high temperature when it continues to work, which affects the judgment of thermal runaway warning. The combustible gas detection method is limited by the low sensitivity of the detector, the limited types of detectable gases, and the high cost, and the actual application effect is not good. Summary of the invention

[0003] The present invention solves the problem that the actual application effect of the current monitoring of battery thermal runaway is poor, and proposes an early warning method and system for pressure release in the early stage of thermal runaway of a lithium battery. The early warning function of thermal runaway is realized without installing complex sensing equipment, and the van der Waals equation that conforms to the actual gas state is used to calculate the gas volume in the battery pack to improve the accuracy of the forecast.

[0004] In order to achieve the above objectives, the following technical solutions are proposed: A method for early warning of pressure release in the early stage of thermal runaway of a lithium battery comprises the following steps: S1, obtaining the pressure and temperature of the gas in the battery pack; S2, calculate the amount of gas substance using the van der Waals equation; S3, calculating the increase in the amount of gaseous material within a set time; S4, determine whether the increase is greater than the increase threshold, if so, it is considered that initial thermal runaway has occurred; if not, return to S1.

[0005] When the exhaust valve opens or the sealing edge ruptures in the early stage of thermal runaway of the battery, causing gas to overflow, the amount of gas in the battery pack increases rapidly. When the gas volume increase and / or growth rate exceeds the threshold value set in the battery management system, i.e., the BMS system program, it can be judged that the battery is depressurized, i.e., the initial thermal runaway occurs, so that the BMS sends an early warning signal for thermal runaway before the dangerous state intensifies. The present invention comprehensively analyzes the air pressure and air temperature data in the battery pack, and uses the van der Waals equation that conforms to the actual gas state to calculate the gas volume in the battery pack, thereby improving the accuracy of the forecast. Moreover, the present invention does not install complex sensing equipment while realizing the early warning function of thermal runaway, and does not change the existing structure of the battery pack, which is convenient for upgrading the safety of battery packs that have been mass-produced or in use, and has practical application significance.

[0006] Preferably, S3 also includes the following steps: using the increase in the amount of gaseous material within the set time to calculate the increase in the amount of gaseous material within the set time, S4 only determines whether the growth rate is greater than the growth rate threshold, if so, it is considered that initial thermal runaway has occurred; if not, return to S1.

[0007] Preferably, S3 also includes the following steps: calculating the increase in the amount of gaseous material within the set time using the increase in the amount of gaseous material within the set time, and S4 judging whether the increase or the growth rate is greater than the set threshold value, and if so, it is considered that initial thermal runaway has occurred; if not, return to S1.

[0008] Preferably, S3 also includes the following steps: calculating the increase in the amount of gaseous material within the set time using the increase in the amount of gaseous material within the set time, and S4 judging whether both the increase and the growth rate are greater than the set threshold value. If so, it is considered that initial thermal runaway has occurred; if not, return to S1.

[0009] Preferably, the increase in the amount of the gas substance is equal to the difference between the amount of the gas substance after a set time has passed and the amount of the gas substance at an initial moment.

[0010] Preferably, the increasing rate of the amount of the gas substance is equal to the quotient of the increase in the amount of the gas substance and the set time.

[0011] Preferably, the van der Waals equation calculation process is as follows: The first product is calculated as the product of the constant measuring the intermolecular attraction and the square of the amount of gas substance; Calculating a first quotient as a quotient of the first product and the square of the volume of the gas in the battery pack; Calculate the first sum as the sum of the collected gas pressure in the battery pack and the first quotient; The second product is calculated as the product of the amount of gas substance and the constant of volume per mol of gas molecules; Calculating the first difference as the difference between the gas volume in the battery pack and the second product; Calculate the third product as the product of the first sum and the first difference; The fourth product is calculated as the product of the amount of gas substance, the molar gas constant and the thermodynamic temperature of the collected gas; Construct the equation so that the third product equals the fourth product and solve for the amount of gaseous substance.

[0012] Preferably, the increase threshold and the speed increase threshold are adjusted according to the warning sensitivity.

[0013] Preferably, the interval of the set time is adjusted according to the warning sensitivity.

[0014] A lithium battery thermal runaway early warning system and a lithium battery thermal runaway early warning method include a BMU control module, the BMU control module is electrically connected to a gas pressure sensor and a gas temperature sensor, the gas pressure sensor and the gas temperature sensor are arranged inside the battery pack, respectively collecting the pressure and temperature of the gas in the battery module.

[0015] The beneficial effects of the present invention are as follows: the present invention comprehensively analyzes the air pressure and air temperature data in the battery pack, and uses the van der Waals equation that conforms to the actual gas state to calculate the gas volume in the battery pack, thereby improving the accuracy of the forecast. Moreover, the present invention does not add complex sensing equipment while realizing the early warning function of thermal runaway, and does not change the existing structure of the battery pack, which is convenient for safety upgrades of battery packs that have been mass-produced or in use, and has practical application significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the method flow of Example 1.

[0017] Figure 2 This is the method flow of Example 2.

[0018] Figure 3 This is the method flow of Example 3.

[0019] Figure 4 This is the method flow of Example 4.

[0020] Figure 5 It is a system configuration diagram of the present invention.

[0021] Among them: 1. Battery pack; 2. Battery module; 3. Gas pressure sensor; 4. Gas temperature sensor; 5. BMU control module. DETAILED DESCRIPTION

[0022] Embodiment 1: This embodiment proposes an early warning method for pressure release in the early stage of thermal runaway of a lithium battery, referring to Figure 1 , including the following steps: S1, collect the air pressure data and air temperature data of the air pressure in the lithium battery pack, install a gas pressure sensor 3 and a gas temperature sensor 4 in the battery pack, and respectively collect the pressure P and temperature T data of the gas in the pack in real time; upload the air pressure and air temperature data: upload the above collected data to the BMU control module 5; S2, calculate the amount of gaseous substances based on the van der Waals equation and the acquired air pressure and temperature data; The van der Waals equation is as follows: Where: n is the amount of gas in the battery pack, in mol; P is the gas pressure, in Pa; V is the gas volume in the battery pack, which is a certain value after the battery pack is assembled, in m 3 ; R is the molar gas constant, its value is 8.314J / mol·K; T is the thermodynamic temperature of the gas, the unit is K; a is the constant that measures the intermolecular attraction, the unit is b is a constant representing the volume of each mol of gas molecules, in m 3 .

[0023] The van der Waals equation calculation process is as follows: Calculate the first product n 2 a: the product of the constant a that measures the attraction between molecules and the square of the amount of gas substance n; Calculate the first quotient First product n 2 a and the square of the gas volume in the battery pack V 2 commerce; Calculate the first sum The gas pressure p in the battery pack collected is of and; Calculate the second product nb: the product of the amount of gas substance n and the constant b of the volume per mol of gas molecules; Calculate the first difference V-nb: the difference between the gas volume V in the battery pack and the second product nb; Calculate the third product First and The product of the first difference V-nb; Calculate the fourth product nRT: the product of the amount of gas substance n, the molar gas constant R, and the thermodynamic temperature T of the collected gas; Constructing Equations The third product Equal to the fourth product nRT. Except for the unknown amount of gas substance n in the equation, the other parameters are all known. Solve the linear equation of one variable and find the amount of gas substance n.

[0024] S3, setting a time interval t, and calculating the increase Δn of the amount of gas substance within the time interval t; Δn=n t -n0; Where: t is the set time interval, in seconds; Δn is the amount of gas substance increase at time t, in mol; n t is the amount of gas substance calculated at time t, in mol; n0 is the amount of gas substance calculated before time t, in mol.

[0025] S4, determine whether the increase Δn is greater than the set increase threshold Δn alert If so, the BMU control module 5 determines that the battery has thermal runaway and sends a thermal runaway warning signal k=1 to the BMS system; if not, the BMU control module 5 determines that the battery is in a normal state, sends a thermal runaway warning value k=0 to the BMS system, and returns to S1; the BMS system determines whether the acquired thermal runaway warning signal k is equal to 0. If so, the BMS system does not issue a thermal runaway warning to the outside and continues to monitor the battery status. The battery system does not take any safety protection action and returns to S1; if not, the BMS system issues a battery thermal runaway warning. After the alarm is issued, the battery system takes safety protection actions such as disconnecting from the grid, forcibly shutting down the power, starting the fire protection cooling system, and starting ventilation.

[0026] This embodiment also proposes an early warning system for thermal runaway of lithium batteries, including a gas pressure sensor 3, a gas temperature sensor 4 and a BMU control module 5. The gas pressure sensor 3 and the gas temperature sensor 4 are both arranged inside the battery pack 1. The gas pressure sensor 3 is used to collect the pressure of the gas in the battery module 2 inside the battery pack 1. The gas temperature sensor 4 is used to collect the temperature of the gas in the battery module 2 inside the battery pack 1. The gas pressure sensor 3 and the gas temperature sensor 4 are installed in the empty position in the battery pack to collect the air pressure and air temperature data in the battery pack in real time, and transmit the data to the control module 5 through the communication line; the BMU control module 5 transmits information with the battery management system, i.e., the BMS system. The alarm threshold Δn is written in advance in the BMS system program. alert .

[0027] The working principle of the present invention is as follows: When all cells are not depressurized, the amount of gas inside the battery pack remains constant because it is a closed space. According to the van der Waals equation, although the air pressure P and temperature T change due to the continuous operation of the battery, the calculated gas amount n remains unchanged, Δn is approximately 0 mol, v n Approximately 0 mol / s. To avoid false alarms, the alarm threshold Δn alert It can be set to a fixed value slightly greater than 0. In this case, Δn<Δn alert, the BMU control module determines that the battery is in a normal state and sends a thermal runaway warning value k=0 to the BMS system. The BMS system does not issue a battery thermal runaway warning and continues to monitor the battery status. The battery system does not take any safety action.

[0028] When a single cell is depressurized due to excessive internal gas pressure, a large amount of gas, such as hydrogen, carbon monoxide, carbon dioxide, methane, hydrogen fluoride, sulfur dioxide, etc., is generated due to the decomposition of the electrolyte, causing the amount of gas in the battery pack to increase rapidly. At this time, the gas amount n calculated by the van der Waals equation increases, making Δn>Δn alert The BMU control module determines that the battery has thermal runaway and sends a thermal runaway warning value k=1 to the BMS system. The BMS system issues a battery thermal runaway warning. After receiving the warning, the battery system takes safety protection actions such as disconnecting the grid, forcibly disconnecting the power, turning on the fire-fighting cooling system, and turning on ventilation. These measures can effectively prevent or mitigate the occurrence of accidents and are conducive to improving the safety of the battery system during use.

[0029] The present invention comprehensively analyzes the air pressure and temperature data in the battery pack, and uses the van der Waals equation that conforms to the actual gas state to calculate the gas volume in the battery pack, thereby improving the accuracy of the forecast. In addition, the present invention does not install complex sensing equipment while realizing the early warning function of thermal runaway, and does not change the existing structure of the battery pack, which is convenient for safety upgrades of battery packs that have been mass-produced or in use, and has practical application significance.

[0030] Embodiment 2: This embodiment is an alternative to embodiment 1, which adopts the speed increase instead of the increment to make a judgment, and proposes an early warning method for pressure release in the early stage of thermal runaway of a lithium battery. Figure 2 , including the following steps: S1, collect the air pressure data and air temperature data of the air pressure in the lithium battery pack, install a gas pressure sensor 3 and a gas temperature sensor 4 in the battery pack, and respectively collect the pressure P and temperature T data of the gas in the pack in real time; upload the air pressure and air temperature data: upload the above collected data to the BMU control module 5; S2, calculate the amount of gaseous substances based on the van der Waals equation and the acquired air pressure and temperature data; The van der Waals equation is as follows: Where: n is the amount of gas in the battery pack, in mol; P is the gas pressure, in Pa; V is the gas volume in the battery pack, which is a certain value after the battery pack is assembled, in m 3 ; R is the molar gas constant, its value is 8.314J / mol·K; T is the thermodynamic temperature of the gas, the unit is K; a is the constant that measures the intermolecular attraction, the unit is b is a constant representing the volume of each mol of gas molecules, in m 3 .

[0031] The van der Waals equation calculation process is as follows: Calculate the first product n 2 a: the product of the constant a that measures the attraction between molecules and the square of the amount of gas substance n; Calculate the first quotient First product n 2 a and the square of the gas volume in the battery pack V 2 commerce; Calculate the first sum The gas pressure p in the battery pack collected is of and; Calculate the second product nb: the product of the amount of gas substance n and the constant b of the volume per mol of gas molecules; Calculate the first difference V-nb: the difference between the gas volume V in the battery pack and the second product nb; Calculate the third product First and The product of the first difference V-nb; Calculate the fourth product nRT: the product of the amount of gas substance n, the molar gas constant R, and the thermodynamic temperature T of the collected gas; Constructing Equations The third product Equal to the fourth product nRT. Except for the unknown amount of gas substance n in the equation, the other parameters are all known. Solve the linear equation of one variable and find the amount of gas substance n.

[0032] S3, setting a time interval t, and calculating the increase Δn of the amount of gas substance within the time interval t; Δn=n t -n0; Where: t is the set time interval, in seconds; Δn is the amount of gas substance increase at time t, in mol; n t is the amount of gas substance calculated at time t, in mol; n0 is the amount of gas substance calculated before time t, in mol.

[0033] The increase in the amount of the gas substance within the set time is calculated using the increase in the amount of the gas substance within the set time; v n =n t -n0 / t; Where: v n It is the rate of increase of the amount of gas substance at time t, in mol / s.

[0034] S4, determine the rate of increase of the amount of gas v n Is it greater than the set speed threshold v? alert If so, the BMU control module 5 determines that the battery has thermal runaway and sends a thermal runaway warning signal k=1 to the BMS system; if not, the BMU control module 5 determines that the battery is in a normal state, sends a thermal runaway warning value k=0 to the BMS system, and returns to S1; the BMS system determines whether the acquired thermal runaway warning signal k is equal to 0. If so, the BMS system does not issue a thermal runaway warning to the outside and continues to monitor the battery status. The battery system does not take any safety protection action and returns to S1; if not, the BMS system issues a battery thermal runaway warning. After the alarm is issued, the battery system takes safety protection actions such as disconnecting from the grid, forcibly shutting down the power, starting the fire protection cooling system, and starting ventilation.

[0035] This embodiment also proposes an early warning system for thermal runaway of lithium batteries, including a gas pressure sensor 3, a gas temperature sensor 4 and a BMU control module 5. The gas pressure sensor 3 and the gas temperature sensor 4 are both arranged inside the battery pack 1. The gas pressure sensor 3 is used to collect the pressure of the gas in the battery module 2 inside the battery pack 1. The gas temperature sensor 4 is used to collect the temperature of the gas in the battery module 2 inside the battery pack 1. The gas pressure sensor 3 and the gas temperature sensor 4 are installed in the empty position in the battery pack to collect the air pressure and air temperature data in the battery pack in real time, and transmit the data to the control module 5 through the communication line; the BMU control module 5 transmits information with the battery management system, i.e., the BMS system. Write the alarm threshold v in advance in the BMS system program alert .

[0036] The working principle of the present invention is as follows: When all cells are not depressurized, the amount of gas inside the battery pack remains constant because it is a closed space. According to the van der Waals equation, although the air pressure P and temperature T change due to the continuous operation of the battery, the calculated gas amount n remains unchanged, Δn is approximately 0 mol, v n Approximately 0 mol / s. To avoid false alarms, the alarm threshold v alert It can be set to a constant value slightly greater than 0. n <v alert , the BMU control module determines that the battery is in a normal state and sends a thermal runaway warning value k=0 to the BMS system. The BMS system does not issue a battery thermal runaway warning and continues to monitor the battery status. The battery system does not take any safety action.

[0037] When a single cell is depressurized due to excessive internal gas pressure, a large amount of gas, such as hydrogen, carbon monoxide, carbon dioxide, methane, hydrogen fluoride, sulfur dioxide, etc., is generated due to the decomposition of the electrolyte, causing the amount of gas in the battery pack to increase rapidly. At this time, the gas amount n calculated by the van der Waals equation increases, making v n >v alert The BMU control module determines that the battery has thermal runaway and sends a thermal runaway warning value k=1 to the BMS system. The BMS system issues a battery thermal runaway warning. After receiving the warning, the battery system takes safety protection actions such as disconnecting the grid, forcibly disconnecting the power, turning on the fire-fighting cooling system, and turning on ventilation. These measures can effectively prevent or mitigate the occurrence of accidents and are conducive to improving the safety of the battery system during use.

[0038] The present invention comprehensively analyzes the air pressure and temperature data in the battery pack, and uses the van der Waals equation that conforms to the actual gas state to calculate the gas volume in the battery pack, thereby improving the accuracy of the forecast. In addition, the present invention does not install complex sensing equipment while realizing the early warning function of thermal runaway, and does not change the existing structure of the battery pack, which is convenient for safety upgrades of battery packs that have been mass-produced or in use, and has practical application significance.

[0039] Embodiment 3: This embodiment detects the increment and the speed increase simultaneously on the basis of Embodiment 1 and Embodiment 2, and proposes an early warning method for pressure release in the early stage of thermal runaway of a lithium battery. Figure 3 , including the following steps: S1, collect the air pressure data and air temperature data of the air pressure in the lithium battery pack, install a gas pressure sensor 3 and a gas temperature sensor 4 in the battery pack, and respectively collect the pressure P and temperature T data of the gas in the pack in real time; upload the air pressure and air temperature data: upload the above collected data to the BMU control module 5; S2, calculate the amount of gaseous substances based on the van der Waals equation and the acquired air pressure and temperature data; The van der Waals equation is as follows: Where: n is the amount of gas in the battery pack, in mol; P is the gas pressure, in Pa; V is the gas volume in the battery pack, which is a certain value after the battery pack is assembled, in m 3 ; R is the molar gas constant, its value is 8.314J / mol·K; T is the thermodynamic temperature of the gas, the unit is K; a is the constant that measures the intermolecular attraction, the unit is b is a constant representing the volume of each mol of gas molecules, in m 3 .

[0040] The van der Waals equation calculation process is as follows: Calculate the first product n 2 a: the product of the constant a that measures the attraction between molecules and the square of the amount of gas substance n; Calculate the first quotient First product n 2 a and the square of the gas volume in the battery pack V 2 commerce; Calculate the first sum The gas pressure p in the battery pack collected is of and; Calculate the second product nb: the product of the amount of gas substance n and the constant b of the volume per mol of gas molecules; Calculate the first difference V-nb: the difference between the gas volume V in the battery pack and the second product nb; Calculate the third product First and The product of the first difference V-nb; Calculate the fourth product nRT: the product of the amount of gas substance n, the molar gas constant R, and the thermodynamic temperature T of the collected gas; Constructing Equations The third product Equal to the fourth product nRT. Except for the unknown amount of gas substance n in the equation, the other parameters are all known. Solve the linear equation of one variable and find the amount of gas substance n.

[0041] S3, setting a time interval t, and calculating the increase Δn of the amount of gas substance within the time interval t; Δn=n t -n0; Where: t is the set time interval, in seconds; Δn is the amount of gas substance increase at time t, in mol; n t is the amount of gas substance calculated at time t, in mol; n0 is the amount of gas substance calculated before time t, in mol.

[0042] The increase in the amount of the gas substance within the set time is calculated using the increase in the amount of the gas substance within the set time; v n =n t -n0 / t; Where: v n It is the rate of increase of the amount of gas substance at time t, in mol / s.

[0043] S4, determine whether the increase or growth rate is greater than the set threshold. If so, the BMU control module 5 determines that the battery has thermal runaway and sends a thermal runaway warning signal k=1 to the BMS system; if not, the BMU control module 5 determines that the battery is in a normal state, sends a thermal runaway warning value k=0 to the BMS system, and returns to S1; the BMS system determines whether the acquired thermal runaway warning signal k is equal to 0. If so, the BMS system does not issue a thermal runaway warning to the outside and continues to monitor the battery status. The battery system does not take safety protection actions and returns to S1; if not, the BMS system issues a battery thermal runaway warning. After the alarm is issued, the battery system takes safety protection actions such as disconnecting the grid, forcibly shutting down the power, turning on the fire protection cooling system, and turning on ventilation.

[0044] This embodiment also proposes an early warning system for thermal runaway of lithium batteries, including a gas pressure sensor 3, a gas temperature sensor 4 and a BMU control module 5. The gas pressure sensor 3 and the gas temperature sensor 4 are both arranged inside the battery pack 1. The gas pressure sensor 3 is used to collect the pressure of the gas in the battery module 2 inside the battery pack 1. The gas temperature sensor 4 is used to collect the temperature of the gas in the battery module 2 inside the battery pack 1. The gas pressure sensor 3 and the gas temperature sensor 4 are installed in the empty position in the battery pack to collect the air pressure and air temperature data in the battery pack in real time, and transmit the data to the control module 5 through the communication line; the BMU control module 5 transmits information with the battery management system, i.e., the BMS system. The alarm threshold Δn is written in advance in the BMS system program. alert and v alert .

[0045] The working principle of the present invention is as follows: When all cells are not depressurized, the amount of gas inside the battery pack remains constant because it is a closed space. According to the van der Waals equation, although the air pressure P and temperature T change due to the continuous operation of the battery, the calculated gas amount n remains unchanged, Δn is approximately 0 mol, v n Approximately 0 mol / s. To avoid false alarms, the alarm threshold Δn alert or v alert It can be set to a fixed value slightly greater than 0. In this case, Δn<Δn alert or v n <v alert , the BMU control module determines that the battery is in a normal state and sends a thermal runaway warning value k=0 to the BMS system. The BMS system does not issue a battery thermal runaway warning and continues to monitor the battery status. The battery system does not take any safety action.

[0046] When a single cell is depressurized due to excessive internal gas pressure, a large amount of gas, such as hydrogen, carbon monoxide, carbon dioxide, methane, hydrogen fluoride, sulfur dioxide, etc., is generated due to the decomposition of the electrolyte, causing the amount of gas in the battery pack to increase rapidly. At this time, the gas amount n calculated by the van der Waals equation increases, making Δn>Δn alert or v n >v alert The BMU control module determines that the battery has thermal runaway and sends a thermal runaway warning value k=1 to the BMS system. The BMS system issues a battery thermal runaway warning. After receiving the warning, the battery system takes safety protection actions such as disconnecting the grid, forcibly disconnecting the power, turning on the fire-fighting cooling system, and turning on ventilation. These measures can effectively prevent or mitigate the occurrence of accidents and are conducive to improving the safety of the battery system during use.

[0047] The present invention comprehensively analyzes the air pressure and temperature data in the battery pack, and uses the van der Waals equation that conforms to the actual gas state to calculate the gas volume in the battery pack, thereby improving the accuracy of the forecast. In addition, the present invention does not install complex sensing equipment while realizing the early warning function of thermal runaway, and does not change the existing structure of the battery pack, which is convenient for safety upgrades of battery packs that have been mass-produced or in use, and has practical application significance.

[0048] Embodiment 4: This embodiment takes both the increment and the speed increase into consideration on the basis of Embodiment 3, and proposes an early warning method for pressure release in the early stage of thermal runaway of a lithium battery. Figure 4 , including the following steps: S1, collect the air pressure data and air temperature data of the air pressure in the lithium battery pack, install a gas pressure sensor 3 and a gas temperature sensor 4 in the battery pack, and respectively collect the pressure P and temperature T data of the gas in the pack in real time; upload the air pressure and air temperature data: upload the above collected data to the BMU control module 5; S2, calculate the amount of gaseous substances based on the van der Waals equation and the acquired air pressure and temperature data; The van der Waals equation is as follows: Where: n is the amount of gas in the battery pack, in mol; P is the gas pressure, in Pa; V is the gas volume in the battery pack, which is a certain value after the battery pack is assembled, in m 3 ; R is the molar gas constant, its value is 8.314J / mol·K; T is the thermodynamic temperature of the gas, the unit is K; a is the constant that measures the intermolecular attraction, the unit is b is a constant representing the volume of each mol of gas molecules, in m 3 .

[0049] The van der Waals equation calculation process is as follows: Calculate the first product n 2 a: the product of the constant a that measures the attraction between molecules and the square of the amount of gas substance n; Calculate the first quotient First product n 2 a and the square of the gas volume in the battery pack V 2 commerce; Calculate the first sum The gas pressure p in the battery pack collected is of and; Calculate the second product nb: the product of the amount of gas substance n and the constant b of the volume per mol of gas molecules; Calculate the first difference V-nb: the difference between the gas volume V in the battery pack and the second product nb; Calculate the third product First and The product of the first difference V-nb; Calculate the fourth product nRT: the product of the amount of gas substance n, the molar gas constant R, and the thermodynamic temperature T of the collected gas; Constructing Equations The third product Equal to the fourth product nRT. Except for the unknown amount of gas substance n in the equation, the other parameters are all known. Solve the linear equation of one variable and find the amount of gas substance n.

[0050] S3, setting a time interval t, and calculating the increase Δn of the amount of gas substance within the time interval t; Δn=n t -n0; Where: t is the set time interval, in seconds; Δn is the amount of gas substance increase at time t, in mol; n t is the amount of gas substance calculated at time t, in mol; n0 is the amount of gas substance calculated before time t, in mol.

[0051] The increase in the amount of the gas substance within the set time is calculated using the increase in the amount of the gas substance within the set time; v n =n t -n0 / t; Where: v n It is the rate of increase of the amount of gas substance at time t, in mol / s.

[0052] S4, determine whether the increase and the growth rate are both greater than the set threshold value. If so, the BMU control module 5 determines that the battery has thermal runaway and sends a thermal runaway warning signal k=1 to the BMS system; if not, the BMU control module 5 determines that the battery is in a normal state, sends a thermal runaway warning value k=0 to the BMS system, and returns to S1; the BMS system determines whether the acquired thermal runaway warning signal k is equal to 0. If so, the BMS system does not issue a thermal runaway warning to the outside and continues to monitor the battery status. The battery system does not take safety protection actions and returns to S1; if not, the BMS system issues a battery thermal runaway warning. After the alarm is issued, the battery system takes safety protection actions such as disconnecting the grid, forcibly shutting down the power, turning on the fire protection cooling system, and turning on ventilation.

[0053] This embodiment also proposes an early warning system for thermal runaway of lithium batteries, including a gas pressure sensor 3, a gas temperature sensor 4 and a BMU control module 5. The gas pressure sensor 3 and the gas temperature sensor 4 are both arranged inside the battery pack 1. The gas pressure sensor 3 is used to collect the pressure of the gas in the battery module 2 inside the battery pack 1. The gas temperature sensor 4 is used to collect the temperature of the gas in the battery module 2 inside the battery pack 1. The gas pressure sensor 3 and the gas temperature sensor 4 are installed in the empty position in the battery pack to collect the air pressure and air temperature data in the battery pack in real time, and transmit the data to the control module 5 through the communication line; the BMU control module 5 transmits information with the battery management system, i.e., the BMS system. The alarm threshold Δn is written in advance in the BMS system program. alert and v alert .

[0054] The working principle of the present invention is as follows: When all cells are not depressurized, the amount of gas inside the battery pack remains constant because it is a closed space. According to the van der Waals equation, although the air pressure P and temperature T change due to the continuous operation of the battery, the calculated gas amount n remains unchanged, Δn is approximately 0 mol, v n Approximately 0 mol / s. To avoid false alarms, the alarm threshold Δn alert and v alert It can be set to a fixed value slightly greater than 0. In this case, Δn<Δn alert And v n <v alert , the BMU control module determines that the battery is in a normal state and sends a thermal runaway warning value k=0 to the BMS system. The BMS system does not issue a battery thermal runaway warning and continues to monitor the battery status. The battery system does not take any safety action.

[0055] When a single cell is depressurized due to excessive internal gas pressure, a large amount of gas, such as hydrogen, carbon monoxide, carbon dioxide, methane, hydrogen fluoride, sulfur dioxide, etc., is generated due to the decomposition of the electrolyte, causing the amount of gas in the battery pack to increase rapidly. At this time, the gas amount n calculated by the van der Waals equation increases, making Δn>Δn alert And v n >v alert The BMU control module determines that the battery has thermal runaway and sends a thermal runaway warning value k=1 to the BMS system. The BMS system issues a battery thermal runaway warning. After receiving the warning, the battery system takes safety protection actions such as disconnecting the grid, forcibly disconnecting the power, turning on the fire-fighting cooling system, and turning on ventilation. These measures can effectively prevent or mitigate the occurrence of accidents and are conducive to improving the safety of the battery system during use.

[0056] The present invention comprehensively analyzes the air pressure and temperature data in the battery pack, and uses the van der Waals equation that conforms to the actual gas state to calculate the gas volume in the battery pack, thereby improving the accuracy of the forecast. In addition, the present invention does not install complex sensing equipment while realizing the early warning function of thermal runaway, and does not change the existing structure of the battery pack, which is convenient for safety upgrades of battery packs that have been mass-produced or in use, and has practical application significance.

Claims

1. A method for early warning of pressure release in the early stage of thermal runaway of a lithium battery, characterized in that: The following steps are involved: S1, obtaining the pressure and temperature of the gas in the battery pack; S2, calculate the amount of gas substance using the van der Waals equation; S3, calculating the increase in the amount of gaseous material within a set time; S4, determine whether the increase is greater than the increase threshold, if so, it is considered that initial thermal runaway has occurred; if not, return to S1.

2. The early warning method for early stage pressure release of lithium battery thermal runaway according to claim 1, characterized in that: The S3 also includes the following steps: using the increase in the amount of gaseous material within the set time to calculate the increase in the amount of gaseous material within the set time, the S4 only determines whether the increase in speed is greater than the increase in speed threshold, if so, it is considered that initial thermal runaway occurs; if not, return to S1.

3. The early warning method for early stage pressure release of lithium battery thermal runaway according to claim 1, characterized in that: The S3 also includes the following steps: using the increase in the amount of gaseous material within the set time to calculate the increase in the amount of gaseous material within the set time, the S4 determines whether the increase or the growth rate is greater than the set threshold, if so, it is considered that initial thermal runaway has occurred; if not, return to S1.

4. The early warning method for early stage pressure release of lithium battery thermal runaway according to claim 1, characterized in that: The S3 also includes the following steps: using the increase in the amount of gaseous material within the set time to calculate the increase in the amount of gaseous material within the set time, the S4 determines whether the increase and the growth rate are both greater than the set threshold value, if so, it is considered that initial thermal runaway has occurred; if not, return to S1.

5. The early warning method for early stage pressure release of lithium battery thermal runaway according to claim 1, characterized in that: The increase in the amount of the gas substance is equal to the difference between the amount of the gas substance after a set time has passed and the amount of the gas substance at an initial moment.

6. The early warning method for early stage pressure release of lithium battery thermal runaway according to claim 2, characterized in that: The increasing rate of the amount of the gas substance is equal to the quotient of the increase in the amount of the gas substance and the set time.

7. A method for early warning of pressure release in the early stage of thermal runaway of a lithium battery according to any one of claims 1 to 6, characterized in that: The van der Waals equation calculation process is as follows: The first product is calculated as the product of the constant measuring the intermolecular attraction and the square of the amount of gas substance; Calculating a first quotient as a quotient of the first product and the square of the volume of the gas in the battery pack; Calculate the first sum as the sum of the collected gas pressure in the battery pack and the first quotient; The second product is calculated as the product of the amount of gas substance and the constant of volume per mol of gas molecules; Calculating the first difference as the difference between the gas volume in the battery pack and the second product; Calculate the third product as the product of the first sum and the first difference; The fourth product is calculated as the product of the amount of gas substance, the molar gas constant and the thermodynamic temperature of the collected gas; Construct the equation so that the third product equals the fourth product and solve for the amount of gaseous substance.

8. The early warning method for early stage pressure release of thermal runaway of a lithium battery according to claim 3 or 4, characterized in that: The increase threshold and the speed increase threshold are adjusted according to the warning sensitivity.

9. The early warning method for early stage pressure release of thermal runaway of a lithium battery according to claim 3 or 4, characterized in that: The interval of the set time is adjusted according to the warning sensitivity.

10. An early warning system for early stage pressure relief of a lithium battery during thermal runaway, applicable to the early warning method for early stage pressure relief of a lithium battery during thermal runaway as claimed in claim 1, characterized in that: The invention comprises a BMU control module (5), wherein the BMU control module (5) is electrically connected to a gas pressure sensor (3) and a gas temperature sensor (4), wherein the gas pressure sensor (3) and the gas temperature sensor (4) are arranged inside the battery pack (1) to respectively collect the pressure and temperature of the gas in the battery module (2).

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