CN110828935B - Safety protection method for lithium ion battery electric vehicle - Google Patents
Safety protection method for lithium ion battery electric vehicle Download PDFInfo
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 39
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 39
- 238000000034 method Methods 0.000 title claims abstract description 34
- 230000004044 response Effects 0.000 claims abstract description 48
- 238000001816 cooling Methods 0.000 claims abstract description 42
- 239000003507 refrigerant Substances 0.000 claims abstract description 19
- 239000007921 spray Substances 0.000 claims abstract description 12
- WVSNNWIIMPNRDB-UHFFFAOYSA-N 1,1,1,3,3,4,4,5,5,6,6,6-dodecafluorohexan-2-one Chemical compound FC(F)(F)C(=O)C(F)(F)C(F)(F)C(F)(F)C(F)(F)F WVSNNWIIMPNRDB-UHFFFAOYSA-N 0.000 claims description 38
- 239000003795 chemical substances by application Substances 0.000 claims description 26
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 230000007613 environmental effect Effects 0.000 claims description 3
- 238000009834 vaporization Methods 0.000 claims description 3
- 230000008016 vaporization Effects 0.000 claims description 3
- 230000008901 benefit Effects 0.000 claims description 2
- 239000003792 electrolyte Substances 0.000 claims description 2
- 230000007480 spreading Effects 0.000 claims description 2
- 238000003892 spreading Methods 0.000 claims description 2
- 238000003860 storage Methods 0.000 claims description 2
- 239000002826 coolant Substances 0.000 claims 1
- 230000008569 process Effects 0.000 abstract description 6
- 238000013461 design Methods 0.000 abstract description 5
- 238000011081 inoculation Methods 0.000 abstract description 5
- 238000011161 development Methods 0.000 abstract description 3
- 230000010354 integration Effects 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 5
- 230000009467 reduction Effects 0.000 description 5
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- 210000004027 cell Anatomy 0.000 description 4
- 230000007246 mechanism Effects 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 238000009529 body temperature measurement Methods 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000020169 heat generation Effects 0.000 description 2
- 230000002427 irreversible effect Effects 0.000 description 2
- 238000005316 response function Methods 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- 239000000779 smoke Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 description 1
- 206010000369 Accident Diseases 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
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- 238000009826 distribution Methods 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
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- 238000012806 monitoring device Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
- 239000002341 toxic gas Substances 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/60—Heating or cooling; Temperature control
- H01M10/61—Types of temperature control
- H01M10/613—Cooling or keeping cold
-
- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62C—FIRE-FIGHTING
- A62C3/00—Fire prevention, containment or extinguishing specially adapted for particular objects or places
- A62C3/16—Fire prevention, containment or extinguishing specially adapted for particular objects or places in electrical installations, e.g. cableways
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/60—Heating or cooling; Temperature control
- H01M10/62—Heating or cooling; Temperature control specially adapted for specific applications
- H01M10/625—Vehicles
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/60—Heating or cooling; Temperature control
- H01M10/63—Control systems
- H01M10/635—Control systems based on ambient temperature
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/60—Heating or cooling; Temperature control
- H01M10/65—Means for temperature control structurally associated with the cells
- H01M10/656—Means for temperature control structurally associated with the cells characterised by the type of heat-exchange fluid
- H01M10/6567—Liquids
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention relates to a safety protection method of a lithium ion battery electric automobile, which mainly comprises a secondary response mode. The first-level response is rapid cooling when the lithium ion battery abnormally generates heat and heats, and the second-level response is efficient fire extinguishing and cooling when the lithium ion battery is out of control due to heat. The first-stage response and the second-stage response adopt the same hardware design and mainly comprise a pump set, a spray head, a refrigerant, a temperature sensor, a CO sensor, a control unit and the like. The method is based on the design of the battery pack of the lithium ion battery electric vehicle, can aim at different characteristics of the inoculation and development process of the lithium ion battery thermal runaway, and can carry out multi-level and all-around protection on the safety of the battery through the integration of cooling before the thermal runaway, extinguishing fire when the thermal runaway and cooling after the fire extinguishment.
Description
Technical Field
The invention belongs to the technical field of safety, relates to a safety protection method for an electric vehicle, and particularly relates to a safety protection method capable of realizing secondary response to thermal runaway of a lithium ion battery of electric vehicle transfer.
Background
In recent years, with global warming and environmental problems such as haze weather, the demand of each country for new energy industry is increasing. And the lithium ion battery is outstanding in the new energy industry due to the excellent performances of large energy density, low self-discharge rate and the like. At present, the annual constants of lithium ion batteries and lithium ion electric vehicles in China show a trend of increasing year by year. However, due to the special properties of the lithium ion battery, when the lithium ion battery is in an abuse state, a heat accumulation condition is easily formed, irreversible decomposition reaction is promoted to occur in the battery, a large amount of heat and combustible gas are released in a short time, once the combustible gas is ignited, the temperature of the battery is exponentially increased, and the battery is considered to be thermally out of control. At the present stage, the fire accidents of the electric automobile show a trend of rising year by year, so that the safety protection problem of the lithium ion battery assembled in the electric automobile is a technical problem to be solved urgently. The safety protection strategy with high efficiency and intelligence is configured on the lithium ion electric vehicle, and has important significance for safe and high-efficiency operation of the electric vehicle.
At present, most of safety protection strategies of lithium ion battery electric vehicles are focused on passive protection, and active protection strategies are few. The existing lithium ion battery safety protection strategy mainly has the following defects: (1) Most of the existing lithium ion battery safety protection strategies act after thermal runaway of the battery, and the occurrence of the thermal runaway cannot be effectively prevented or inhibited. (2) The existing safety protection method mostly aims at extinguishing the open fire, and does not consider the characteristic that the surface of the battery still has higher temperature after the open fire is extinguished. Namely, after the open fire of the batteries is extinguished, the possibility of thermal runaway propagation still exists among the non-thermal runaway batteries of the same module. (3) Most of fire extinguishing systems in the existing lithium ion battery safety protection strategies only aim at a single battery module, and the battery is extremely easy to spread to a module close to normal work due to open fire.
Aiming at the characteristic of thermal runaway of the lithium ion battery, the invention provides a more intelligent, systematic and efficient safety protection method, namely the safety protection method has two-stage response and can realize rapid external cooling intervention when the battery abnormally generates heat; the safety protection device is characterized by comprising a multi-position integrated safety protection design which can quickly extinguish open fire when the battery is out of thermal control and quickly cool down after the open fire is extinguished.
Disclosure of Invention
The invention aims to provide a safety protection method for a lithium ion electric vehicle, which carries out multi-level and all-around protection on the safety of a battery by implementing various response strategies such as temperature reduction before thermal runaway, fire extinguishment during thermal runaway, temperature reduction after fire extinguishment and the like in the inoculation and development process of the thermal runaway of the lithium ion battery. The invention solves the problems that: the safety protection method for the lithium ion battery electric vehicle is provided, intervention is performed in advance when abnormal heat is generated in the early stage of thermal runaway of the battery, and heat of the battery is taken away through a refrigerant, so that the thermal runaway of the battery is prevented. Further, when the thermal runaway of the battery occurs, the fire extinguishing medium is released to a fire point through the spray head, and the open fire of the battery is quickly extinguished. And finally, after the battery is extinguished, the refrigerant is released again, the heat generated by the battery after extinguishment is taken away, and the propagation of thermal runaway between different batteries of the same module and even between different modules is prevented.
In order to solve the above problems and achieve the above object, the present invention has the technical solution: a safety protection method for an electric automobile with a lithium ion battery. The safety protection method mainly comprises two stages of response mechanisms, namely, one-stage response: rapidly cooling the lithium ion battery when the lithium ion battery abnormally generates heat; secondary response: high-efficiency fire extinguishing and rapid cooling when the lithium ion battery is out of control due to heat.
The first-order response is the rapid cooling when the lithium ion battery abnormally generates heat. For a battery management system, the upper limit of the operating range is 60 ℃, and once the battery temperature exceeds the upper limit of the battery management system, the battery management system will power down or shut down. Thus, the primary response is primarily directed to cells that abnormally generate heat. The primary response function is realized mainly by hardware devices such as a pump, a spray head, a refrigerant, a temperature sensor, a control unit and the like.
Furthermore, the type of the pump is determined according to the releasing pressure requirement of the refrigerant and the atomizing requirement of the nozzle. The pump outlet pressure should be calculated according to the following equation (1):
P＝H·ρ (1)
wherein H is the head of the water pump, m; p is outlet pressure, pa; rho is density of refrigerant, kg/m 3 。
Furthermore, the spray head should be an atomizing spray head.
Furthermore, in the method, the refrigerant and the fire extinguishing medium are both perfluorohexanone. The perfluorohexanone is a colorless transparent liquid at normal temperature, is suitable for transportation and storage, and has no leakage risk. The perfluorohexanone has large heat absorption capacity and good insulation property, and is very suitable for cooling the battery in a normal working state. Meanwhile, the vapor pressure of the perfluorohexanone is 12 times that of water, and the perfluorohexanone can be quickly gasified and diffused to a fire extinguishing space after being released, so that the perfluorohexanone is particularly suitable for extinguishing fire in a cavity.
Furthermore, in order to enable temperature measurement to be more accurate, temperature signals used by the BMS system and the temperature sensors are provided together.
Furthermore, in order to make the temperature measurement result more accurate, the temperature sensor is a contact temperature sensor. The distribution points are located at the bus bars of the batteries.
Furthermore, the control unit receives signals of the temperature sensor and the BMS, judges and sends signals to the pump, and controls the release of the perfluorohexanone refrigerant. Meanwhile, a fault signal is sent to the BMS, and a driver is required to park in time to evacuate passengers for checking.
Further, the turn-on preset temperature is generally a temperature at which the SEI film is decomposed. The temperature at which the SEI film decomposes varies slightly depending on different material systems. At present, the temperature for the SEI film decomposition is generally recognized to be about 70-80 ℃, so in order to reduce the irreversible damage to the battery and reduce the probability of false alarm as much as possible, the opening temperature of the cooling system is 80 +/-10 ℃. The judgment conditions in this section are shown in the following formula (2):
[T BMS ,T sensor ] max >80±10℃ (2)
wherein, T BMS Maximum battery temperature, deg.c, detected by the BMS system; t is sensor The maximum battery temperature detected by the temperature sensor is DEG C; [] max The operation is maximum value operation;
furthermore, the amount of the refrigerant is calculated according to the heat generation amount of the battery. In order to save the cost of the fire extinguishing agent, the part is calculated by the using amount of the fire extinguishing agent of the single battery cell. As shown in the following formulas (3) to (4):
c·m·ΔT 1 ＝Q C6F12O (3)
wherein c is the specific heat of the battery and is generally 1.1kJ/kg DEG C; m is the battery mass, kg; delta T 1 The temperature of the battery is reduced, here to 45 ℃;
Q C6F12O ＝Q 1 +Q 2 (4)
wherein Q is C6F12O Total heat absorbed for perfluorohexanone, Q 1 Is the latent heat of perfluorohexanone, Q 2 The sensible heat of perfluorohexanone was calculated according to equations (5) to (6), respectively:
Q 1 ＝C·W·ΔT 2 (5)
Q 2 ＝γ·W (6)
wherein C is the specific heat of the perfluorohexanone and is 1.013kJ/kg DEG C; w is the refrigerant dosage, kg; delta T 2 Is the temperature rise of perfluorohexanone, 24.5 ℃ in this process. Gamma is the heat of vaporization of perfluorohexanone, 88.0kJ/kg.
Further, after the refrigerant is released, the battery may be accompanied by a temperature rising process, and therefore, a feedback cooling mechanism is arranged in the battery cooling device. After cooling down at every turn is accomplished, the controller all can receive BMS's temperature signal, and when the temperature signal received was greater than the default, cooling system can restart again, and when the temperature that the controller received was less than or equal to the default, cooling system no longer worked. The amount of refrigerant required for the feedback part is described in the embodiment section. The feedback multi-time cooling function can ensure the effectiveness of a cooling system and block thermal runaway in the inoculation stage.
Further, if some battery systems are powered off when the system temperature is higher than 60 ℃, a separate temperature monitoring device can be arranged, and a fire protection system is adopted to supply power to replace the BMS system to realize the temperature monitoring function.
Further, when the amount of perfluorohexanone released by the primary response exceeds 15% of the total design amount of the secondary response, the feedback cooling is not performed on the primary response in order to prevent the insufficient amount of perfluorohexanone used by the secondary response. When the primary response fails, if the heat exchange condition is not changed at the moment, the temperature of the battery is likely to further rise, a series of reactions in the battery are triggered, and the temperature of the battery continues to rise and generate a series of characteristic gases. The secondary response triggers when the cell surface temperature and CO concentration reach the threshold of the secondary response.
The secondary response is high-efficiency fire extinguishing and rapid cooling when the lithium ion battery is out of control due to heat. The secondary response mainly corresponds to safety protection after thermal runaway of the battery. The realization of the secondary response function mainly depends on hardware equipment such as a pump, a spray head, a fire extinguishing medium, a BMS system, a temperature sensor, a CO sensor, a control unit and the like.
Furthermore, the pump, the spray head and the fire extinguishing medium used in the secondary response are the same as those of the primary response. In order to reduce the complexity of the system, the differentiation of each level of response is realized at the software level, and each level of response uses the same hardware control system.
Further, a secondary response is triggered by a temperature sensor, a CO sensor and a control unit.
Further, the temperature trigger signal is provided by the temperature sensor and the BMS system together. The temperature trigger signal mainly comprises an absolute temperature value and a temperature rise rate.
Furthermore, the absolute value of the trigger temperature of the secondary response is 150-200 ℃, and the temperature rise rate is 1.0 ℃/s. The absolute values of the thermal runaway temperatures of batteries of different systems are different and can be flexibly adjusted according to actual conditions. The triggering CO concentration of the secondary response is determined according to the experimental cavity.
Further, the amount of perfluorohexanone fire extinguishing agent in the module in which thermal runaway of the battery occurs should be determined according to the following method:
the extinguishing concentration of the perfluorohexanone for extinguishing the lithium ion battery electrolyte fire at the present stage is about 6.2-6.7%, and the dosage W of the extinguishing agent is W according to the extinguishing concentration 1 The following formula (7) should be specified according to NFPA 2001:
W 1 ＝(V/S)[E/(100-E)] (7)
wherein E is the fire extinguishing concentration,%; v is the volume of the protected zone, m 3 (ii) a W is the amount of the fire extinguishing agent, kg; s is the specific volume of the superheated steam of the fire extinguishing agent under the atmospheric pressure of 101kPa and the lowest environmental temperature of the protection area, m 3 Kg, which should be calculated according to the following formula (8):
S＝0.0664+0.0002741t (8)
wherein t is the lowest ambient temperature, deg.C.
Furthermore, in the method, the fire extinguishing concentration is designed to be 8% in order to keep a safety margin.
Further, after secondary response is triggered, in order to prevent the battery open fire from spreading among battery boxes with different temperatures, all the battery boxes simultaneously spray the perfluorohexanone fire extinguishing agent, and the fire extinguishing concentration of each battery box is sprayed to 8%, according to the existing theory, when the perfluorohexanone concentration reaches 8%, the open fire combustion cannot be supported in the cavity.
Further, the fire extinguishing concentration is reached after the default fire extinguishing agent is released, and the open fire disappears. At the moment, the fire extinguishing agent is released again in the module with thermal runaway, the heat of the battery after fire extinguishment is taken away, the temperature reduction of the battery after fire extinguishment is accelerated, and the battery afterburning and thermal runaway propagation are prevented.
Furthermore, each releasing line is provided with a one-way valve to prevent the fire extinguishing agent from flowing back.
Furthermore, in order to prevent the branch controller from being burnt out by a large-range fire, the check valve is a normally-open check valve controlled by a customized battery.
Further, the electromagnetic check valve is controlled by a branch controller.
Wherein, in order to reduce the electromagnetic interference that a plurality of solenoid valves produced in the course of working, carry on the electromagnetic shielding and earthing to each battery valve.
Further, the amount of the fire extinguishing agent used in the secondary response portion can be calculated according to the following two methods.
The method comprises the following steps: the calculation can be based on the balance of heat production during thermal runaway of the cell and heat absorption by the fire suppressant. As shown in the following formula (9),
Q t1 ＝Q C6F12O ＝112.8185W 2 (9)
wherein Q is C6F12O Heat absorbed for perfluorohexanone, kJ; q t1 kJ, the heat released in the thermal runaway process of the battery; w is a group of 2 Is the amount of perfluorohexanone in kg calculated according to the thermal runaway heat production heat balance.
Further, W calculated by the method is not considered to be reduced heat generation due to reduction of reaction in the battery after inhibition of thermal runaway of the battery, as compared with the actual case 2 Compared with the actual situation, the dosage is larger.
The second method comprises the following steps: the calculation can be made based on the balance between the amount of heat released and the amount of heat absorbed by the fire suppressant as the peak temperature reached after the battery flame is suppressed drops to the desired temperature. As shown in the following formula (10),
Q t2 ＝Q C6F12O ＝112.8185W 3 (10)
wherein Q C6F12O Heat absorbed for perfluorohexanone, kJ; q t2 kJ, the heat released by the battery after the peak temperature reached by the flame is reduced to the desired temperature; w 3 Is the dosage of perfluorohexanone, kg, calculated according to the heat balance of heat production and temperature reduction.
Furthermore, in practical engineering application, the dosage of the fire extinguishing agent for cooling can be comprehensively determined and selected according to various influence factors such as the space reserved for a fire extinguishing system, the cost of the fire extinguishing system, a battery system and the like.
Furthermore, the dosage of the fire extinguishing agent and the refrigerant is determined by controlling the starting time of the pump. The pump on time can be calculated by the following equation (11).
t＝W/Q (11)
Wherein, W is the dosage of the fire extinguishing agent, kg; q is the mass flow of the pump, kg/s; t is time, s.
The invention has the advantages that: 1. the device effectively protects the thermal runaway in multiple stages of the inoculation, development and the like of the thermal runaway. The device can realize multi-level and all-around protection of the lithium ion battery. 2. The device adopts perfluorohexanone spray feedback cooling before thermal runaway. The efficiency and the success rate of cooling are greatly improved, and the abnormal temperature rise of the battery can be effectively controlled. And the perfluorohexanone can not generate smoke and toxic gas after being released, thereby not causing damage to a normal working battery. The cooling system can be prevented from causing panic of passengers while ensuring the normal operation of the system. 3. The device adopts the mode that all the nozzles in the battery boxes spray simultaneously in the fire extinguishing stage, thereby effectively inhibiting the propagation of thermal runaway between different battery boxes.
Drawings
FIG. 1 is a flow chart of a safety protection strategy for a lithium ion battery system of a passenger vehicle;
fig. 2 is a schematic diagram of a two-stage response control.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
When the temperature sensor in the battery box or the BMS system detects that the surface temperature of the battery exceeds 80 +/-10 ℃, the battery is judged to be abnormally heated, and the primary response triggers. The BMS system will send an electrical signal to the master controller, which then sends the signal to the respective level controllers and pumps via the CAN bus. Because all electromagnetism check valves are normally open design, consequently, at this moment, except taking place the branch controller in the battery box of unusual intensification, all can receive main control unit's signal by other branch controllers, close the solenoid valve after the action to prevent that fire extinguishing agent from releasing other battery boxes and causing unnecessary loss, reduce cooling efficiency.
In the first-order response, a feedback cooling mechanism is designed to improve the cooling efficiency. After cooling down at every turn is accomplished, the controller all can receive BMS's temperature signal, and when the temperature signal received was greater than the default, cooling system can restart again, and when the temperature that the controller received was less than or equal to the default, cooling system no longer worked. The feedback multi-time cooling function can ensure the effectiveness of a cooling system and block thermal runaway in the inoculation stage.
It is worth noting that in multiple feedback cooling, the amount of fire extinguishing agent required for each cooling is different because the temperature to which the battery can be raised after each cooling is different. In combination with the above formulas (3) to (6), the amount of the fire extinguishing agent required for each cooling is as shown in the following formula (12):
W cool ＝c·m·(T x -60)/(C·ΔT 2 +γ) (12)
wherein, W cool The amount of fire extinguishing agent required for each cooling, kg; c is the specific heat capacity of the battery, kJ/kg DEG C; t is x C is the specific heat capacity of the fire extinguishing agent, kJ/kg DEG C, which is the temperature fed back by the BMS each time; delta T 2 Is the exotherm for perfluorohexanone, 24.5 ℃ in this process. Gamma is the heat of vaporization of perfluorohexanone, 88.0kJ/kg.
It is noted that the refrigerant in this section is overdesigned in view of the amount of fire suppressant required for feedback control. To simplify control, the dosage of fire suppressant will be determined by the time the pump is on. The pump on time is as follows (13):
t＝∑W cool /Q (13)
wherein, W cool The dosage of the temperature-reducing fire extinguishing agent is kg; q is the mass flow of the pump in kg/s. t is time, s.
When the first-order response can not effectively inhibit the temperature rise of the battery, the temperature of the battery can be further raised until the safety valve is opened or thermal runaway occurs, and at the moment, second-order response is needed, namely, quick fire extinguishing and cooling after the thermal runaway of the battery are realized. If the first-order response cannot effectively block the temperature rise of the battery, the temperature of the battery rises rapidly, and the abnormal temperature rise can continue to be thermal runaway.
After the thermal runaway of the battery, the battery releases a large amount of high-temperature smoke and jet fire is likely to be formed. At this time, the battery may emit a large amount of CO gas, and the battery surface temperature exhibits an exponential rise, and both the absolute value of the battery surface temperature and the temperature rise rate are maintained at extremely high levels. Therefore, we use this feature of thermal runaway of the battery to trigger a secondary response.
In the method, the CO concentration is used for assisting the temperature and temperature rise rate change of the battery as a trigger signal of secondary response. In order to prevent the exhaustion of CO during thermal runaway, the absolute value of temperature and the rate of temperature rise are used as the primary trigger signals in the method, and secondary responses are triggered even if the CO concentration does not reach a threshold value. The reason for using the absolute value of CO concentration-assisted temperature and rate of temperature rise as trigger signals is to advance the time of the early warning.
After the secondary response is triggered, the controller sends an instruction to the pump, and the pump is started. t is t 2 And then, the controller sends signals to all the sub-controllers except the sub-controller of the abnormal battery pack, the solenoid valve receives the sub-controller signals, and the normally open battery valve is closed. t is t 2 Can be calculated according to the following equation (14):
t 2 ＝(n*W 1 )/Q (14)
wherein n is the total number of the battery packs; w 1 The dosage of the single-cell pack fire extinguishing agent is kg calculated according to the fire extinguishing concentration; q is the mass flow of the pump in kg/s. t is time, s.
The significance of the action is two, wherein firstly, the high-temperature and high-pressure gas of the battery pack with thermal runaway is prevented from rushing to other battery packs without runaway to cause the runaway of related batteries; secondly, unnecessary loss of perfluorohexanone can be prevented.
The present embodiments are illustrative only, and do not limit the scope of the invention, and modifications and variations that may be made by those skilled in the art without departing from the principles of the invention are to be considered as within the scope of the invention.
Claims (2)
1. A safety protection method for an electric vehicle with a lithium ion battery is characterized by comprising the following steps: the safety protection method mainly comprises two-stage response, namely rapid cooling when the lithium ion battery abnormally generates heat and efficient fire extinguishing and rapid cooling when the lithium ion battery is out of control in heat;
the first-level response is rapid cooling when the lithium ion battery abnormally generates heat; the primary response has the main functions of quickly releasing a high-efficiency cooling refrigerant when the battery is abnormally heated, taking away the heat of the battery and preventing the battery from being abnormally heated and developing thermal runaway; the first-stage response hardware device mainly comprises a pump set, a spray head, a refrigerant, a temperature sensor and a control unit;
the secondary response is high-efficiency fire extinguishing and rapid cooling when the lithium ion battery is out of control due to heat; the secondary response mainly has the advantages that when the battery is out of control due to thermal runaway, the battery open fire is controlled in a short time, and the damage of battery jet fire to a battery system is reduced; on one hand, fire extinguishing medium is released in other battery modules which are not out of control, so that the propagation and spread of open fire in the battery compartment are prevented; on the other hand, after the open fire of the battery is extinguished, the high-efficiency cooling medium is released, the battery after the fire is extinguished is rapidly cooled, and the thermal runaway is prevented from spreading among different batteries and even among different modules in the module; the hardware device for the secondary response comprises a spray head, a storage tank, a conveying pipeline, a fire extinguishing medium, a temperature sensor, a CO sensor and a control unit;
the refrigerant and the fire extinguishing medium used in the method are all perfluorohexanone; the perfluorohexanone absorbs a large amount of heat after being released;
the amount of the refrigerant is calculated according to the heat production quantity of the battery and is calculated aiming at the amount of the fire extinguishing agent of the single battery cell, and the amount is shown as the following formula 3-4:
c·m·∆T 1 = Q C6F12O formula 3
Wherein c is the specific heat of the battery and is 1.1kJ/kg DEG C; m is the mass of the battery, and the unit is kg; Δ T 1 The temperature of the battery is reduced, here to 45 ℃;
Q C6F12O = Q 1 + Q 2 formula 4
Wherein Q is C6F12O Total heat absorbed for perfluorohexanone, Q 1 Is the latent heat of perfluorohexanone, Q 2 The sensible heat of perfluorohexanone was calculated according to formulas 5 to 6, respectively:
Q 1 = C·W·∆T 2 formula 5
Q 2 = gamma.W type 6
WhereinC is the specific heat of the perfluorohexanone and is 1.013kJ/kg DEG C; w is the amount of refrigerant in kg; Δ T 2 Is the temperature rise of perfluorohexanone, and in the method, the temperature is 24.5 ℃, and gamma is the heat of vaporization of perfluorohexanone and is 88.0kJ/kg.
2. The safety protection method for the lithium ion battery electric vehicle according to claim 1, characterized in that: the amount of perfluorohexanone fire extinguishing agent in the module where thermal runaway of the battery occurs should be determined according to the following method:
the fire extinguishing concentration of the perfluorohexanone for extinguishing the lithium ion battery electrolyte fire at the present stage is 6.2% -6.7%, and according to the fire extinguishing concentration, the dosage W of the fire extinguishing agent 1 The following formula 7 should be specified according to NFPA 2001:
W 1 =(V/S)[E/(100-E)]formula 7
Wherein E is the extinguishing concentration; v is the volume of the protected zone in m 3 (ii) a W is the amount of the fire extinguishing agent in kg; s is the specific volume of the fire extinguishing agent superheated steam under the atmospheric pressure of 101kPa and the environmental temperature of the protection area, and the unit is m 3 Kg, which should be calculated according to the following formula 8:
s =0.0664+0.0002741t formula 8
Where t is the ambient temperature in degrees Celsius.
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