CN110416644B - Vehicle-mounted early warning device for hidden damage monitoring and thermal runaway of lithium ion power battery and early warning method thereof - Google Patents
Vehicle-mounted early warning device for hidden damage monitoring and thermal runaway of lithium ion power battery and early warning method thereof Download PDFInfo
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Classifications
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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
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4207—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells for several batteries or cells simultaneously or sequentially
-
- 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
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
-
- 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
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4285—Testing apparatus
-
- 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
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
- H01M10/482—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte for several batteries or cells simultaneously or sequentially
-
- 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
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
- H01M10/488—Cells or batteries combined with indicating means for external visualization of the condition, e.g. by change of colour or of light density
-
- 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
Abstract
The invention discloses a vehicle-mounted early warning device for hidden damage monitoring and thermal runaway of a lithium ion power battery, which comprises the following components: the carbon dioxide-ethylene combined gas sensor is arranged in the battery pack module and is used for detecting the concentration of carbon dioxide and ethylene gas; the pressure sensor is arranged at the indentation type pressure relief valve of the battery shell and is used for detecting the internal pressure of the battery cell; the filling pipeline is arranged in the battery pack module, foam holes are uniformly formed in the filling pipeline and used for discharging flame-retardant foam; a plurality of solenoid valves disposed at the corresponding foam holes; a flame retardant foam storage tank disposed outside the battery and in communication with the fill line; and the controller is connected with the carbon dioxide-ethylene combined gas sensor, the pressure sensor and the electromagnetic valve and is used for controlling the electromagnetic valve to work. The invention also discloses an early warning method of the vehicle-mounted early warning device for the recessive damage monitoring and the thermal runaway of the lithium ion power battery.
Description
Technical Field
The invention relates to the technical field of vehicle-mounted hidden damage monitoring of lithium ion power batteries, in particular to a vehicle-mounted hidden damage monitoring and early warning device for thermal runaway of a lithium ion power battery and a warning method thereof.
Background
Electrodynamic technology is the future of the automotive industry. As a core component of the electric automobile, the safety of the power battery is an important consideration of the electric automobile, and the active safety protection measure of the prospective power battery is realized, so that the popularization of the electric automobile can be greatly promoted. The lithium ion battery has been the mainstream choice of the power battery for vehicles by virtue of its advantages of high capacity, high output voltage, high charging rate, high energy density, low self-discharge, excellent cycle characteristics, and the like. However, the high activity of the electrode material and the flammability of the electrolyte material thereof determine the risk of thermal runaway of the lithium ion battery. In recent years, with the increase of market preservation quantity and improvement of power performance of electric vehicles, serious safety accidents caused by thermal runaway of vehicle-mounted lithium ion power batteries frequently occur, and the confidence of consumers on the electric vehicles is seriously hit. The practical and effective improvement of the thermal runaway safety performance of the vehicle-mounted lithium ion power battery by engineering means has become one of the most urgent technical demands in the current new energy automobile industry.
Structurally, lithium ion batteries include both active and inactive components, i.e., reactive cells and other necessary elements. By hidden damage is meant structural damage that is not directly noticeable in the characterization of the parameters outside the cell.
For vehicle-mounted lithium ion power batteries, hidden damage inside the vehicle-mounted lithium ion power batteries is ubiquitous and cannot be completely avoided.
For a battery core formed by laminated winding materials, since a lithium ion battery belongs to an insertion type battery based on the rocking chair principle, even if the battery is completely and normally used, with each charge and discharge, the electrode and the diaphragm in the battery core can be damaged on the surface and structural fatigue, namely aging, caused by stress residues generated by carrier insertion and precipitation. Aging itself is a recessive damage to the battery. When the battery is subjected to slight abuse conditions such as a small amount of overcharging and the like, the aging process of the battery core is aggravated by the slight structural damage of the battery, so that irreversible damage occurs. Therefore, for lithium ion power batteries, the use process is a process of accumulation of hidden damage of the battery cells. For inactive components other than the cells, there are a number of sealing and connecting components that are spot welded, laser welded, glued, bolted or even riveted. The extrusion, impact and vibration of the external force may deform or fail. Because the failure occurs on the nonfunctional structure, the external parameters of the battery are not significantly changed at the time of occurrence, and the working condition of causing similar conditions cannot be completely avoided in the actual use of the electric vehicle.
Hidden damage inside the battery is one of the important causes of thermal runaway or spontaneous combustion of the battery.
Studies have shown that the occurrence of thermal runaway is highly correlated with internal short circuits in batteries, and damage to the internal structure of the batteries becomes a direct cause of the occurrence of internal short circuits. For the battery core, the hidden damage of the interface between the electrode and the diaphragm can lead to uneven deposition of carriers, induce dendrite generation and further improve the occurrence probability of internal short circuit; the hidden damage of the diaphragm can obviously weaken the safety of the battery core, and the occurrence probability of short circuit in the battery under extreme working conditions is increased. For the inactive components, since the vehicle-mounted power battery is integrated into a battery pack with an output voltage of 360 to 480 volts step by step in use, failure of any connecting piece and sealing piece can cause local electric spark to occur, so that the battery cell is in an extreme working condition of electric shock or thermal shock, and the thermal runaway of the battery is directly triggered.
Thermal runaway occurs with greater hysteresis than recessive damage occurs, such as spontaneous combustion, and there is difficulty in determining early damaged monomers in an on-board environment, and non-real-time invasive probing means are not of engineering significance.
Studies have shown that there is a large time difference between the occurrence of damage to the internal structure of the battery and the occurrence of abnormality of its external parameters that can be recognized by the BMS (battery management system). When the external parameters of the battery are abnormal, the occurrence of thermal runaway of the battery is near to the eye, and the early warning window of the battery safety system is greatly reduced. In addition, in actual production of the electric vehicle, a large number of battery cells are packaged in a stack form in a battery pack, and are thus integrated into a power pack of the electric vehicle. The prior battery hidden damage research is realized by observing the morphological characteristics of the electrode surface after the single body is disassembled. The invasive probing means is not of engineering significance in the practical level of electric vehicles. How to determine the hidden damaged single body from the nearly thousand batteries in working state by a non-destructive means under the condition that the external parameters are not changed, and evaluate the damage degree, and the method is still in a technical blank state at present.
The internal hidden damage of the battery is identified, so that early warning time of thermal runaway can be advanced, and an intervention time window of the thermal runaway safety intervention measure is remarkably enlarged.
Studies have shown that when an existing on-board system detects that thermal runaway is imminent, it alerts that thermal runaway is occurring at intervals of only about 30 seconds. The active safety measures are difficult to fully play roles, and the control panel of the BMS is rapidly damaged by the high heat of the battery, so that the system is offline, and the operation of the active safety system of the vehicle-mounted battery is interrupted. The hidden damage of the battery can be identified in advance, the battery can actively give an alarm to the vehicle-mounted system before high heat is generated, the safety of the BMS control circuit is ensured, the vehicle-mounted active safety is timely activated, the timeliness and the effectiveness of the intervention of the active safety measure under the potential dangerous working condition are ensured, and the life and property safety of a driver is ensured to the greatest extent.
Disclosure of Invention
The invention aims to design and develop a vehicle-mounted lithium ion power battery hidden damage monitoring and early warning device, which can detect the concentration of carbon dioxide and ethylene gas in a battery pack module and the internal pressure of a battery monomer in real time, determine the hidden damage degree of the vehicle-mounted lithium ion power battery and improve the driving safety.
The invention further aims to design and develop an early warning method of the vehicle-mounted hidden damage monitoring and early warning device for the lithium ion power battery, which can collect the concentration of carbon dioxide and ethylene gas in a battery pack module and the internal pressure of a battery monomer, and determine the working state of an electromagnetic valve based on a BP neural network.
According to the invention, the injection quantity of the flame-retardant foam can be accurately controlled according to the concentration of carbon dioxide and ethylene gas in the collected battery pack module and the internal pressure of the battery monomer, so that the thermal runaway of the battery can be avoided, the flame-retardant foam can be directly injected into the target module, and other intact battery modules can be stored to the greatest extent.
The technical scheme provided by the invention is as follows:
an on-vehicle lithium ion power battery recessive damage monitoring and early warning device of thermal runaway includes:
the battery pack modules are internally and uniformly provided with battery monomers;
the plurality of carbon dioxide-ethylene combined gas sensors are respectively arranged in the corresponding battery pack modules, are in one-to-one correspondence with the battery monomers and are used for detecting the concentration of carbon dioxide and ethylene gas;
the pressure sensors are respectively arranged at indentation type pressure relief valves of the shell of the battery cell and are used for detecting the internal pressure of the battery cell;
the filling pipeline is communicated with the battery pack module, and foam holes are respectively formed in the filling pipeline positioned in the battery pack module and used for discharging flame-retardant foam;
a plurality of solenoid valves disposed at the corresponding foam holes;
a flame retardant foam storage tank disposed outside the battery and in communication with the fill line;
and the controller is connected with the carbon dioxide-ethylene combined gas sensor, the pressure sensor and the electromagnetic valve and is used for receiving detection data of the carbon dioxide-ethylene combined gas sensor and the pressure sensor and controlling the electromagnetic valve to work.
Preferably, the pressure sensor is arranged at a bulge of an indentation type pressure release valve of the battery unit, which is close to one side of the battery top cover; and foam holes are respectively arranged on the filling pipelines in the battery pack module.
Preferably, the system further comprises an alarm device connected with the controller and used for receiving the data of the controller and giving an alarm.
An early warning method of a vehicle-mounted lithium ion power battery recessive damage monitoring and thermal runaway early warning device collects the concentration of carbon dioxide and ethylene gas in a battery pack module and the internal pressure of a battery monomer, and determines the working state of an electromagnetic valve based on a BP neural network, comprising the following steps:
measuring the concentration of carbon dioxide and ethylene gas in a battery pack module and the internal pressure of a battery monomer through a sensor according to a sampling period;
step two, determining an input layer neuron vector x= { x of the three-layer BP neural network 1 ,x 2 ,x 3 -a }; wherein x is 1 Is the concentration of carbon dioxide, x in the module where the battery cell is located 2 Is the concentration of ethylene gas, x in the module where the battery cell is located 3 Is the internal pressure of the battery cell;
wherein the input layer neurons x i ＝{x i1 ,x i2 ,...,x iM I= {1,2,3} where M is the number of battery cells;
mapping the input layer vector to hidden layers, wherein m neurons are arranged in the hidden layers;
step four, obtaining an output layer neuron vector o= { o 1 ,o 2 -a }; wherein o is 1 Is the working state of the electromagnetic valve o 2 The neuron value of the output layer is as follows N is the number of electromagnetic valves, which is the same as the number of the modules in the battery pack, W j In the working state of the j-th electromagnetic valve, when W j When=1, the j-th electromagnetic valve is in an open state, when W j When=0, the j-th electromagnetic valve is in a closed state; the neuron value of the output layer is +.>When o 2 When the battery cell damage alarm is carried out by the alarm device when the battery cell damage alarm is in the range of (1), when o 2 When the number of the codes is =2, the alarm device carries out the damage alarm of the tightness of the battery module, when o 2 When the temperature is=3, the alarm device gives a thermal runaway risk alarm, and when o 2 When=0, the alarm device does not alarm.
Preferably, when the internal pressure of the battery cell satisfies:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
determining the corresponding W j =1, and controls the injection amount of the flame retardant foam as follows:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stable data for item i, m r For the injection amount of the flame-retardant foam, m max For maximum injection of flame retardant foam, p 0 Is at standard atmospheric pressure;
the alarm device carries out thermal runaway risk alarm, reminds a driver to stop by the side, and withdraws.
Preferably, when the internal pressure of the battery cell satisfies:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
determining the corresponding W j =1, and controls the injection amount of the flame retardant foam as follows:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stable data for item i, m r For the injection amount of the flame-retardant foam, m max Is the maximum injection amount of the flame retardant foam;
the alarm device carries out thermal runaway risk alarm, reminds the driver to stop immediately and withdraws.
Preferably, when the internal pressure of the battery cell satisfies:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stability data for item i;
the electromagnetic valve does not work, and the alarm device gives an alarm of battery monomer damage, reminds a driver to stop the vehicle by side and checks the vehicle.
Preferably, when the internal pressure of the battery cell satisfies:
and the concentration change of carbon dioxide in the battery pack module meets the following conditions:
the concentration change of ethylene in the battery pack module meets the following conditions:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery 1 Is the detection data of the concentration of carbon dioxide in the module where the battery monomer is located, x 10 Is the historical stable data of the concentration of carbon dioxide in the module where the battery monomer is located, x 2 Is the detection data of the concentration of ethylene gas in the module where the battery monomer is located, x 20 Historical stable data of the concentration of ethylene gas in the module where the battery monomer is located;
the electromagnetic valve does not work, and the alarm device carries out the damage alarm of the tightness of the battery module to remind a driver to stop the vehicle by the side and check the vehicle.
Preferably, the hidden layer has 5 neurons.
Preferably, the excitation functions of the hidden layer and the output layer both adopt S-shaped functions f j (x)＝1/(1+e -x )。。
The beneficial effects of the invention are as follows:
(1) The vehicle-mounted lithium ion power battery hidden damage monitoring and early warning device for thermal runaway, which is designed and developed by the invention, can detect the concentration of carbon dioxide and ethylene gas in the battery pack module and the internal pressure of a battery monomer in real time, determine the hidden damage degree of the vehicle-mounted lithium ion power battery and improve the driving safety.
(2) The pressure sensor adopted by the invention is only required to be arranged at the indentation type pressure release valve of the battery monomer, has small volume, can be directly integrated into the battery sealing cap in the battery packaging process, does not relate to the processing of a battery core, does not influence the battery operation, and can be used under the production process and equipment of the existing battery.
(3) The PPM-level high-sensitivity gas sensor used by the invention has small volume, low cost, no dependence on an external power supply, capability of being sealed in a module in battery package packaging, no dependence on external signal output of a battery pack and little influence by external factors; the gas with various characteristics is cooperatively measured, so that the recognition precision is high and the false alarm probability is low.
(4) The invention can identify potential threat and alarm in the very early stage of battery damage which cannot be perceived by the prior art, and can advance the early warning time by a plurality of orders of magnitude, so that active safety intervention of thermal runaway is possible.
(5) The invention is a safety hardware device matched with a vehicle-mounted BMS system, is a safety sub-module specially developed based on the safety requirement of the electric vehicle, is different from the existing safety measures developed for the energy storage power station, emphasizes the compatibility with the existing control software of the electric vehicle, and gives consideration to the internal structural layout and the dynamic requirement of the electric vehicle.
(6) The early warning method of the early warning device for the recessive damage monitoring and the thermal runaway of the vehicle-mounted lithium ion power battery, which is designed and developed by the invention, can collect the concentration of carbon dioxide and ethylene gas in the battery pack module and the internal pressure of a battery monomer, and determine the working state of the electromagnetic valve based on the BP neural network. The injection quantity of the flame-retardant foam can be accurately controlled according to the concentration of carbon dioxide and ethylene gas in the collected battery pack module and the internal pressure of the battery monomer, so that thermal runaway of the battery can be avoided, the flame-retardant foam can be directly injected into the target module, and other intact battery modules can be stored to the greatest extent.
Drawings
Fig. 1 is a schematic diagram of a general process of thermal runaway occurrence according to the present invention.
Fig. 2 is a schematic diagram showing the voltage and temperature changes with time during the battery overcharge thermal runaway side reaction process according to the present invention.
Fig. 3 is a schematic representation of the battery change at 103s in fig. 2.
Fig. 4 is a schematic representation of the battery change at 166s in fig. 2.
Fig. 5 is a schematic representation of the battery change at 183s in fig. 2.
Fig. 6 is a schematic representation of the battery change at 197s in fig. 2.
Fig. 7 is a schematic diagram showing analysis of gas components generated by thermal runaway of battery temperature rise according to the present invention.
Fig. 8 is a graph showing the relationship between gas and temperature generated when the temperature of the battery is raised and controlled by thermal runaway according to the present invention.
Fig. 9 is a graph showing the relationship between temperature and time at the time of thermal runaway of battery temperature rise according to the present invention.
Fig. 10 shows the relationship between gas generation and temperature and time during thermal runaway of the battery according to the present invention.
Fig. 11 is a schematic structural diagram of the vehicle-mounted lithium ion power battery hidden damage monitoring and early warning device.
Fig. 12 is a schematic structural diagram of the vehicle-mounted device for monitoring and early warning hidden damage of lithium ion power batteries.
Fig. 13 is a schematic diagram of a blasting structure of the vehicle-mounted lithium ion power battery hidden damage monitoring and early warning device.
Fig. 14 is a schematic view of the thermal runaway development process according to the present invention.
Detailed Description
The present invention is described in further detail below with reference to the drawings to enable those skilled in the art to practice the invention by referring to the description.
As shown in fig. 1, the internal structure of the battery must be damaged to some extent before thermal runaway occurs. As thermal runaway occurs, internal damage continues to expand, triggering larger scale side reactions, and eventually developing to an irreversible extent. For the lithium ion battery with a perfect structure, electrolyte in the battery core does not participate in chemical reaction, and no substance exchange occurs with the outside of the system in the working state. When the lithium ion battery is damaged endangering safety, the electrolyte in the battery cell is subjected to oxidation reaction no matter how tiny the damage is. The oxidation products thereof will exchange substances in gaseous form with the outside world. For this purpose, indentation relief valves are provided on the housing heads of the cells. Meanwhile, as the battery monomer and the battery pack are packaged layer by layer, the environment is relatively sealed and stable. If the integrity of the shell of the damaged monomer is good, the generation of gas inevitably leads to the change of the internal pressure suffered by the indentation of the battery shell; if the outer shell of the damaged cell is communicated with the external environment, the gas composition in the closed battery module changes. Therefore, whether electrolyte decomposition occurs or not can be judged by monitoring disturbance of physical quantity of environmental state in the battery monomer or the module. And further, under the condition of not depending on the external parameter output of the battery, judging whether the battery has structural damage endangering safety or not, and realizing real-time monitoring of hidden damage of the power battery in the working state under the vehicle-mounted environment.
Then, the pressure signal and the gas-sensitive signal are used as characterization, so that the aim of advancing the thermal runaway early warning time can be fulfilled. When thermal runaway occurs, the development process of the thermal runaway can be divided into two stages of flameless combustion and flameless combustion by taking whether the electrode material is decomposed to generate oxygen as a boundary. As particularly shown in fig. 14.
If it is desired to block the progress of thermal runaway, the early warning time of thermal runaway must be before the reaction progresses to flameful combustion. Studies have shown that gas starts to appear inside the cell from the reversible damage of the cell structure. After which gas is continuously generated inside the cell. In the early stages of thermal damage, as shown in stage 1 and stage 2 of fig. 2, there is no significant change in both voltage and temperature of the battery, but if internal pressure of the battery is used as a characterization, a characterization of the occurrence of thermal runaway can be obtained in advance. As shown in fig. 2, the temperature and voltage were significantly changed after 150 seconds of the experiment, and the battery had a visually recognizable internal pressure change characteristic at 103 seconds. If internal short circuit occurs, the integrity of the battery shell is damaged, and is marked as the beginning of thermal runaway, the early warning time of the thermal runaway can be advanced by at least about 60 seconds by using the pressure signal, and the specific change is shown in fig. 3-6.
Studies have shown that when the electrolyte of a vehicle-mounted power battery is oxidatively decomposed, the gaseous products thereof are water, carbon monoxide, carbon dioxide and a small amount of organic vapor. Wherein, carbon dioxide is the main component of the gas product, and the characteristic components are carbon monoxide and hydrofluoric acid steam. The composition of the gas product after thermal runaway of lithium ion batteries with different electrode materials is shown in fig. 7. Wherein, the products of all the electrode materials take carbon dioxide and ethylene steam as main components. Furthermore, the characteristic gas signal is present before the electrolyte reacts. As shown in fig. 1, the decomposition of the SEI marks the beginning of the battery structure damage. Studies have shown that the decomposition of an SEI film (a passivation film layer having solid electrolyte properties) is also accompanied by the occurrence of small amounts of carbon dioxide and ethylene gas. The same gas signal characteristics are also presented in fig. 9. It shows that the sensor detects gas generation at around 100 deg.c of the battery, which coincides with the decomposition temperature of the SEI film. Therefore, by detecting the gas signals of carbon dioxide and ethylene vapor in combination, the occurrence of damage within the cell can be directly characterized very early in the damage. Meanwhile, as reflected in all of fig. 8 to 10, there are 2 peaks in the exhaust gas amount of the battery, wherein the second peak represents the occurrence of thermal runaway. The first significant peak is about 1000 seconds earlier than the second peak. This fully demonstrates the prospective nature of internal pressure and gas sensing methods in thermal runaway warning.
Based on the reasons, the invention adopts the following technical scheme to realize real-time monitoring of hidden damage and early warning of thermal runaway of the vehicle-mounted lithium ion power battery in a working state:
as described above, although the hidden damage of the battery can be more sensitively detected by directly disposing the gas sensor inside the battery cell, the signal extraction thereof is more difficult and the sealability of the battery is damaged because it needs to be disposed above the battery cell. This clearly increases the process requirements and processing costs of the monomer. Therefore, through comprehensive consideration, the method for respectively monitoring the internal pressure of the battery monomer and the carbon dioxide concentration and the characteristic gas content in the sealed battery pack by means of the pressure sensor arranged at the indentation type pressure release valve of the battery shell and the carbon dioxide-ethylene combined gas sensor arranged in the battery pack module realizes the purposes of real-time monitoring of hidden damage and early warning of thermal runaway of the vehicle-mounted lithium ion power battery.
Meanwhile, the monitoring data are transmitted to the singlechip for summarizing by taking the battery pack module as a unit, and then uploaded to an upper computer (controller) comprising the BMS safety sub-module. And comparing the gas-sensitive monitoring data with historical data in the system to judge whether abnormal fluctuation exists in the gas-sensitive monitoring data of the module. If so, the system alarms the driver and determines the position of the monomer with hidden damage in the module according to the internal pressure data of the monomer, so that the system is ready for the intervention of the follow-up active safety measures.
The main components of the device include: the device comprises a strain sensor probe assembly, a carbon dioxide gas sensor probe assembly, a signal transmission assembly, a singlechip, an upper computer and a device box body.
Specifically, in this embodiment, the device includes a plurality of battery pack modules, in which battery cells are uniformly arranged in the battery pack modules, and a plurality of carbon dioxide-ethylene combined gas sensors are respectively disposed in the corresponding battery pack modules, and the battery cells are in one-to-one correspondence and are used for detecting the concentration of carbon dioxide and ethylene gas; the pressure sensors are respectively arranged at indentation type pressure relief valves of the shell of the battery cell and are used for detecting the internal pressure of the battery cell; the filling pipeline (intervention device of the safety measure) is communicated with the inside of the battery pack module, foam holes are respectively formed in the filling pipeline positioned in the battery pack module and used for discharging flame-retardant foam, and preferably, a foam hole is formed in the filling pipeline in each battery coating group and a solenoid valve is correspondingly arranged, so that the control is convenient; the flame-retardant foam storage box is arranged outside the battery and communicated with the filling pipeline, and is used for storing and providing flame-retardant foam; and the controller is connected with the carbon dioxide-ethylene combined gas sensor, the pressure sensor and the electromagnetic valve and is used for receiving detection data of the carbon dioxide-ethylene combined gas sensor and the pressure sensor and controlling the electromagnetic valve to work.
A strain type pressure sensor with the area of 0.5 square cm is arranged at the bulge part of the indentation type pressure release valve of the battery unit, which is close to one side of the battery top cover. The whole battery module is positioned outside the battery sealing body, and leads are led out from the holes of the top cover at four corners and are connected with the battery module control board. The signals are transmitted into the BMS system through the signal path after the modules are assembled. And arranging a PPM sensitivity level ethylene gas sensor and a carbon dioxide sensor probe in the module gas passage, and then leading signals of the PPM sensitivity level ethylene gas sensor and the carbon dioxide sensor probe into the BMS system through the signal passage. And then the purposes of hidden damage monitoring and early warning of thermal runaway are achieved by a method for judging the position of a damaged monomer in the problem module and the pressure sensor judging module through the gas sensor, as shown in figures 11-13.
The vehicle-mounted lithium ion power battery hidden damage monitoring and early warning device for thermal runaway, which is designed and developed by the invention, can detect the concentration of carbon dioxide and ethylene gas in the battery pack module and the internal pressure of a battery monomer in real time, determine the hidden damage degree of the vehicle-mounted lithium ion power battery and improve the driving safety. The pressure sensor adopted by the invention is only required to be arranged at the indentation type pressure release valve of the battery monomer, has small volume, can be directly integrated into the battery sealing cap in the battery packaging process, does not relate to the processing of a battery core, does not influence the battery operation, and can be used under the production process and equipment of the existing battery. The PPM-level high-sensitivity gas sensor used by the invention has small volume, low cost, no dependence on an external power supply, capability of being sealed in a module in battery package packaging, no dependence on external signal output of a battery pack and little influence by external factors; the gas with various characteristics is cooperatively measured, so that the recognition precision is high and the false alarm probability is low. The invention can identify potential threat and alarm in the very early stage of battery damage which cannot be perceived by the prior art, and can advance the early warning time by a plurality of orders of magnitude, so that active safety intervention of thermal runaway is possible.
The invention also provides an early warning method of the early warning device for recessive damage monitoring and thermal runaway of the vehicle-mounted lithium ion power battery, which is used for collecting the concentration of carbon dioxide and ethylene gas in a battery pack module and the internal pressure of a battery monomer and determining the working state of an electromagnetic valve based on a BP neural network, and comprises the following steps:
step one, building a BP neural network model.
The neurons of each layer on the BP model form full interconnection connection, the neurons in each layer are not connected, the output and the input of the neurons of the input layer are the same, namely o i ＝x i . The neurons of the intermediate hidden layer and the output layer have the operating characteristics of
o pj ＝f j (net pj )
Where p represents the current input sample, ω ji To connect weights, o, from neuron i to neuron j pi O, the current input to neuron j pj To its output; f (f) j As a non-linear, slightly non-decreasing function, generally taking the form of an S-shaped function, i.e. f j (x)＝1/(1+e -x )。
The BP network system structure adopted by the invention is composed of three layers, wherein the first layer is an input layer, n nodes are provided, n detection signals representing the working state of equipment are corresponding, and the signal parameters are given by a data preprocessing module; the second layer is a hidden layer, m nodes are all determined in a self-adaptive mode by the training process of the network; the third layer is an output layer, and p nodes are totally determined by the response which is actually required to be output by the system.
The mathematical model of the network is:
input vector: x= (x 1 ,x 2 ,...,x n ) T
Intermediate layer vector: y= (y) 1 ,y 2 ,...,y m ) T
Output vector: o= (o) 1 ,o 2 ,...,o p ) T
In the invention, the number of input layer nodes is n=3, the number of output layer nodes is p=2, and the number of hidden layer nodes is m=5.
The input layer 3 parameters are expressed as: x is x 1 Is the concentration of carbon dioxide, x in the module where the battery cell is located 2 Is the concentration of ethylene gas, x in the module where the battery cell is located 3 Is the internal pressure of the battery cell;
wherein the input layer neurons x i ＝{x i1 ,x i2 ,...,x iM I= {1,2,3} where M is the number of battery cells;
the output layer 2 parameters are expressed as: o (o) 1 Is the working state of the electromagnetic valve o 2 The neuron value of the output layer is as follows N is the number of electromagnetic valves, which is the same as the number of the modules in the battery pack, W j In the working state of the j-th electromagnetic valve, when W j When=1, the j-th electromagnetic valve is in an open state, when W j When=0, the j-th electromagnetic valve is in a closed state; the neuron value of the output layer is +.>When o 2 When the battery cell damage alarm is carried out by the alarm device when the battery cell damage alarm is in the range of (1), when o 2 When the number of the codes is =2, the alarm device carries out the damage alarm of the tightness of the battery module, when o 2 When=3, the alarm device performs thermal runawayRisk alert, when o 2 When the value is=0, the alarm device does not alarm;
wherein if o 2 =3, o 1 =1, i.e. if a thermal runaway alarm is given, the corresponding solenoid valve will operate.
And step two, training the BP neural network.
After the BP neural network node model is established, the BP neural network can be trained. And acquiring a training sample according to historical experience data of the product, and giving a connection weight between the input node i and the hidden layer node j, and a connection weight between the hidden layer node j and the output layer node k.
(1) Training method
Each sub-network adopts a method of independent training; during training, a group of training samples are provided, wherein each sample consists of an input sample and an ideal output pair, and when all actual outputs of the network are consistent with the ideal outputs, the training is finished; otherwise, the ideal output of the network is consistent with the actual output by correcting the weight.
(2) Training algorithm
The BP network adopts an error back propagation (Backward Propagation) algorithm for training, and the steps can be summarized as follows:
the first step: a network with reasonable structure is selected, and initial values of all node thresholds and connection weights are set.
And a second step of: the following calculations are made for each input sample:
(a) Forward calculation: j units to layer l
In the method, in the process of the invention,for the weighted sum of j unit information of layer l in the nth calculation,/>J units and for layer lConnection weight between units i of the previous layer (i.e. layer l-1,), ->For the previous layer (i.e., layer l-1, node number n l-1 ) The working signal sent by the unit i; when i=0, let ∈ -> The threshold for j cells of layer i.
If the activation function of element j is a sigmoid function
And is also provided with
If neuron j belongs to the first hidden layer (l=1), then there is
If neuron j belongs to the output layer (l=l), then there is
And e j (n)＝x j (n)-o j (n)；
(b) Reverse calculation error:
for output units
To hidden unit
(c) Correcting the weight value:
η is the learning rate.
And a third step of: new samples or new period samples are input until the network converges, and the input sequence of the samples in each period is rearranged during training.
The BP algorithm adopts a gradient descent method to solve the extreme value of the nonlinear function, and has the problems of local minimum sinking, low convergence speed and the like. One of the more efficient algorithms is the Levenberg-Marquardt optimization algorithm, which allows for shorter network learning times and can effectively suppress network collapse to a local minimum. The weight adjustment rate is selected as
Δω＝(J T J+μI) -1 J T e
Where J is a Jacobian matrix of error versus weight differentiation, I is an input vector, e is an error vector, and the variable μ is an adaptively adjusted scalar used to determine whether learning is done according to Newton's or gradient methods.
When designing the system, the system model is a network which is only initialized, the weight is required to be learned and adjusted according to the data sample obtained in the using process, and the self-learning function of the system is designed for the system model. Under the condition that the learning samples and the number are specified, the system can perform self-learning to continuously perfect the network performance.
(1) When the internal pressure of the battery cell satisfies:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
determining the corresponding W j =1, and controls the injection amount of the flame retardant foam as follows:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stable data for item i, m r For the injection amount of the flame-retardant foam, m max For maximum injection of flame retardant foam, p 0 Is at standard atmospheric pressure;
the alarm device carries out thermal runaway risk alarm, reminds a driver to stop by the side, and withdraws.
(2) When the internal pressure of the battery cell satisfies:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
determining the corresponding W j =1, and controls the injection amount of the flame retardant foam as follows:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stable data for item i, m r For the injection amount of the flame-retardant foam, m max Is flame retardant foamMaximum injection amount of foam;
the alarm device carries out thermal runaway risk alarm, reminds the driver to stop immediately and withdraws.
(3) When the internal pressure of the battery cell satisfies:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stability data for item i;
the electromagnetic valve does not work, and the alarm device gives an alarm of battery monomer damage, reminds a driver to stop the vehicle by side and checks the vehicle.
(4) When the internal pressure of the battery cell satisfies:
and the concentration change of carbon dioxide in the battery pack module meets the following conditions:
the concentration change of ethylene in the battery pack module meets the following conditions:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery 1 Is the detection data of the concentration of carbon dioxide in the module where the battery monomer is located, x 10 Is the historical stable data of the concentration of carbon dioxide in the module where the battery monomer is located, x 2 Is the detection data of the concentration of ethylene gas in the module where the battery monomer is located, x 20 Historical stable data of the concentration of ethylene gas in the module where the battery monomer is located;
the electromagnetic valve does not work, and the alarm device carries out the damage alarm of the tightness of the battery module to remind a driver to stop the vehicle by the side and check the vehicle.
The method for providing the technical state of the engine according to the present invention is further described below with reference to specific examples.
10 sets of batteries were selected to operate at different temperatures, and the operating states of the 10 sets of batteries were simulated, with specific data shown in table 1.
Table 1 specific battery operation data
| Sequence number | Carbon dioxide concentration | Ethylene gas concentration | Internal pressure of battery cell |
| 1 | 0.02 | 0.01 | 1.01p 0 |
| 2 | 0.12 | 0.2 | 1.2p 0 |
| 3 | 0.05 | 0.06 | 1.1p 0 |
| 4 | 0.12 | 0.08 | 1.18p 0 |
| 5 | 0.1 | 0.11 | 1.20p 0 |
| 6 | 0.22 | 0.20 | 1.28p 0 |
| 7 | 0.35 | 0.42 | 1.41p 0 |
| 8 | 0.28 | 0.15 | 1.30p 0 |
| 9 | 0.13 | 0.22 | 1.22p 0 |
| 10 | 0.20 | 0.19 | 1.20p 0 |
The control is performed by adopting the early warning method provided by the invention, and the specific result is shown in table 2.
The 10 groups of batteries are disassembled in a poor way and observed, the positions of the batteries sprayed with the flame-retardant foam are damaged to different degrees, the positions of the batteries are kept intact, the batteries are not damaged, the batteries are not polluted by the flame-retardant foam, meanwhile, the electrolyte is analyzed, the electrolyte is decomposed to different degrees, if the batteries are not filled with the flame-retardant foam, thermal runaway is likely to happen, and the batteries are very dangerous. Therefore, the early warning method provided by the invention is feasible.
The early warning method of the early warning device for the recessive damage monitoring and the thermal runaway of the vehicle-mounted lithium ion power battery, which is designed and developed by the invention, can collect the concentration of carbon dioxide and ethylene gas in the battery pack module and the internal pressure of a battery monomer, and determine the working state of the electromagnetic valve based on the BP neural network. The injection quantity of the flame-retardant foam can be accurately controlled according to the concentration of carbon dioxide and ethylene gas in the collected battery pack module and the internal pressure of the battery monomer, so that thermal runaway of the battery can be avoided, the flame-retardant foam can be directly injected into the target module, and other intact battery modules can be stored to the greatest extent.
Although embodiments of the present invention have been disclosed above, it is not limited to the details and embodiments shown and described, it is well suited to various fields of use for which the invention would be readily apparent to those skilled in the art, and accordingly, the invention is not limited to the specific details and illustrations shown and described herein, without departing from the general concepts defined in the claims and their equivalents.
Claims (7)
1. An early warning method of a vehicle-mounted lithium ion power battery hidden damage monitoring and thermal runaway early warning device comprises the following steps:
the battery pack modules are internally and uniformly provided with battery monomers;
the plurality of carbon dioxide-ethylene combined gas sensors are respectively arranged in the corresponding battery pack modules, are in one-to-one correspondence with the battery monomers and are used for detecting the concentration of carbon dioxide and ethylene gas;
the pressure sensors are respectively arranged at indentation type pressure relief valves of the shell of the battery cell and are used for detecting the internal pressure of the battery cell;
the filling pipeline is communicated with the battery pack module, and foam holes are respectively formed in the filling pipeline positioned in the battery pack module and used for discharging flame-retardant foam;
a plurality of solenoid valves disposed at the corresponding foam holes;
a flame retardant foam storage tank disposed outside the battery and in communication with the fill line;
the controller is connected with the carbon dioxide-ethylene combined gas sensor, the pressure sensor and the electromagnetic valve, and is used for receiving detection data of the carbon dioxide-ethylene combined gas sensor and the pressure sensor and controlling the electromagnetic valve to work;
the pressure sensor is arranged at a bulge part of the indentation type pressure release valve of the battery monomer, which is close to one side of the battery top cover; a foam hole is respectively arranged on the filling pipeline in the battery pack module;
the alarm device is connected with the controller and used for receiving the data of the controller and giving an alarm;
the method is characterized by collecting the concentration of carbon dioxide and ethylene gas in a battery pack module and the internal pressure of a battery monomer, determining the working state of an electromagnetic valve based on a BP neural network, and comprising the following steps:
measuring the concentration of carbon dioxide and ethylene gas in a battery pack module and the internal pressure of a battery monomer through a sensor according to a sampling period;
step two, determining an input layer neuron vector x= { x of the three-layer BP neural network 1 ,x 2 ,x 3 -a }; wherein x is 1 Is the concentration of carbon dioxide, x in the module where the battery cell is located 2 Is the concentration of ethylene gas, x in the module where the battery cell is located 3 Is the internal pressure of the battery cell;
wherein the input layer neurons x i ＝{x i1 ,x i2 ,...,x iM I= {1,2,3} where M is the number of battery cells;
mapping the input layer vector to hidden layers, wherein m neurons are arranged in the hidden layers;
step four, obtaining an output layer neuron vector o= { o 1 ,o 2 -a }; wherein o is 1 Is the working state of the electromagnetic valve o 2 The neuron value of the output layer is as follows N is the number of electromagnetic valves, which is the same as the number of the modules in the battery pack, W j In the working state of the j-th electromagnetic valve, when W j When=1, the j-th electromagnetic valve is in an open state, when W j When=0, the j-th electromagnetic valve is in a closed state; the neuron value of the output layer is +.>When o 2 When the battery cell damage alarm is carried out by the alarm device when the battery cell damage alarm is in the range of (1), when o 2 When the number of the codes is =2, the alarm device carries out the damage alarm of the tightness of the battery module, when o 2 When the temperature is=3, the alarm device gives a thermal runaway risk alarm, and when o 2 When=0, the alarm device does not alarm.
2. The early warning method of the vehicle-mounted lithium ion power battery hidden damage monitoring and thermal runaway early warning device according to claim 1, wherein when the internal pressure of the battery cell meets the following conditions:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
determining the corresponding W j =1, and controls the injection amount of the flame retardant foam as follows:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stable data for item i, m r For the injection amount of the flame-retardant foam, m max For maximum injection of flame retardant foam, p 0 Is at standard atmospheric pressure;
the alarm device carries out thermal runaway risk alarm, reminds a driver to stop by the side, and withdraws.
3. The early warning method of the vehicle-mounted lithium ion power battery hidden damage monitoring and thermal runaway early warning device according to claim 2, wherein when the internal pressure of the battery cell meets the following conditions:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
determining the corresponding W j =1, and controls the injection amount of the flame retardant foam as follows:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stable data for item i, m r For the injection amount of the flame-retardant foam, m max Is the maximum injection amount of the flame retardant foam;
the alarm device carries out thermal runaway risk alarm, reminds the driver to stop immediately and withdraws.
4. The early warning method of the vehicle-mounted lithium ion power battery hidden damage monitoring and thermal runaway early warning device according to claim 3, wherein when the internal pressure of the battery cell meets the following conditions:
and the concentration of carbon dioxide and ethylene gas in the battery pack module all satisfy:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery i For the detection data of item i, x i0 Historical stability data for item i;
the electromagnetic valve does not work, and the alarm device gives an alarm of battery monomer damage, reminds a driver to stop the vehicle by side and checks the vehicle.
5. The method for early warning of a recessive damage monitoring and thermal runaway early warning device for a vehicle-mounted lithium ion power battery according to claim 4, wherein when the internal pressure of the battery cell meets the following conditions:
and the concentration change of carbon dioxide in the battery pack module meets the following conditions:
the concentration change of ethylene in the battery pack module meets the following conditions:
wherein x is 3 X is the detection data of the internal pressure of the battery 30 X is the historical stable data of the internal pressure of the battery 1 Is the detection data of the concentration of carbon dioxide in the module where the battery monomer is located, x 10 Is the historical stable data of the concentration of carbon dioxide in the module where the battery monomer is located, x 2 Is the detection data of the concentration of ethylene gas in the module where the battery monomer is located, x 20 Historical stable data of the concentration of ethylene gas in the module where the battery monomer is located;
the electromagnetic valve does not work, and the alarm device carries out the damage alarm of the tightness of the battery module to remind a driver to stop the vehicle by the side and check the vehicle.
6. The method for early warning of a hidden damage monitoring and thermal runaway early warning device for a vehicle-mounted lithium ion power battery according to claim 5, wherein the number of neurons in the hidden layer is 5.
7. The method for early warning of a hidden damage monitoring and thermal runaway early warning device for a vehicle-mounted lithium-ion power battery according to claim 6, wherein the excitation functions of the hidden layer and the output layer are S-shaped functions f j (x)＝1/(1+e -x )。
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| CN114559815A (en) * | 2020-11-27 | 2022-05-31 | 李玉钦 | New energy automobile battery thermal runaway judging and handling method |
| CN112510278A (en) * | 2020-11-30 | 2021-03-16 | 同济大学 | Thermal runaway detection and processing method and system for vehicle-mounted lithium ion power battery pack |
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