Battery thermal runaway multi-stage early warning device and control method thereof

Abstract

A battery thermal runaway multi-stage early warning device and its control method belong to the technical field of lithium ion power battery safety monitoring. In the device, the capacitor displacement sensor adopts a parallel plate capacitor structure to monitor the deformation of the battery cell; the three-layer step temperature sensor is composed of three layers of temperature changing materials arranged in concentric circles, independently outputs step signals of three temperature nodes of 85 DEG C, 135 DEG C and 200 DEG C, and realizes the internal temperature monitoring of the battery; the pressure sensor of the pressure relief valve film monitors the pressure change at the battery pressure relief valve. After the signals of various sensors are collected and processed, they are input into the logic judgment unit, combined with the multi-signal composite judgment to output the three-stage early warning signal, and then driven by the isolation driving unit to drive the corresponding LED indication. The valve adopts triple sensing fusion and pure hardware logic hierarchical judgment, realizes accurate early warning of early, middle and late thermal runaway, has fast response speed, high reliability, compact structure and is suitable for various batteries, and can effectively improve the safety of battery use.

Description

Technical Field

[0001] This invention relates to the technical field of safety monitoring of lithium-ion power batteries, and more particularly to a multi-level early warning device for battery thermal runaway and its control method. Background Technology

[0002] Driven by energy transition, the new energy vehicle and energy storage power station industries have developed rapidly. Lithium-ion batteries, with their high energy density and long cycle life, have become the mainstream power source and energy storage carrier. However, during use, lithium-ion batteries are prone to thermal runaway due to factors such as mechanical abuse, electrical abuse, or thermal abuse, leading to serious safety accidents such as battery fires and explosions. Furthermore, during thermal runaway, complex chain chemical reactions occur inside the battery, releasing large amounts of flammable and toxic gases and particulate matter. If timely warnings and interventions are not implemented, this can cause fires to spread, environmental pollution, and personal injury. Therefore, deeply understanding the evolution of thermal runaway in lithium-ion batteries and developing efficient and reliable early warning devices based on this understanding is of great significance for improving the active safety of battery systems.

[0003] Currently, commercial battery thermal runaway early warning mainly relies on a single temperature sensor to monitor abnormal changes in battery surface temperature or voltage. However, temperature signals exhibit significant lag; by the time the surface temperature rises significantly, the battery has often already entered the mid-to-late stages of thermal runaway. Voltage signals show little change in the early stages of a sudden internal short circuit, making early warning difficult. Furthermore, existing pressure monitoring solutions mostly employ traditional MEMS pressure sensors, which are costly, structurally complex, and output continuous analog signals, requiring signal processing circuits and algorithms for judgment, increasing system complexity and the risk of false alarms. Single-sensor monitoring methods cannot comprehensively capture the multi-physics field changes in the early stages of thermal runaway, resulting in slow early warning response and low accuracy, failing to meet the high safety standards required for batteries in energy storage power stations and electric vehicles. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a multi-level early warning device and control method for battery thermal runaway. Based on the staged characteristics of the thermal runaway evolution process, a multi-level early warning device integrating a three-layer step-temperature sensor and a pressure relief valve membrane pressure sensor is proposed. The three-layer step-temperature sensor corresponds to three key temperature nodes in the initial stage of thermal runaway (SEI membrane decomposition), the middle stage (diaphragm melting), and the outbreak stage (internal short circuit), realizing graded perception of the thermal runaway process. The pressure relief valve membrane pressure sensor uses graphite nanosheets / PDMS porous conductive foam material, which is in a low-resistance conductive state under normal conditions. When the pressure relief valve is opened, the high-pressure gas impact causes the conductive network to break, resulting in an order-of-magnitude jump in resistance and outputting a switching alarm signal. The two sensors work together, combined with a capacitive displacement sensor to monitor the bulging deformation of the shell, forming a three-dimensional monitoring network integrating multiple parameters such as gas pressure, temperature, and deformation. This enables early warning and stage identification of the entire thermal runaway process, significantly improving the timeliness and reliability of the warning and reducing the risk of false alarms and missed alarms.

[0005] The technical solution of the present invention to solve the problem of early warning of thermal runaway of power battery is to provide a multi-parameter fusion early warning system for thermal runaway of battery that integrates a capacitor displacement sensor, a battery internal temperature monitoring device and a pressure relief valve diaphragm pressure sensor. The system includes a capacitor displacement sensor, a battery internal temperature monitoring device and a pressure relief valve diaphragm pressure sensor, a signal acquisition and processing unit, a logic judgment unit, an isolation drive unit and an indication unit.

[0006] The capacitive displacement sensor is integrally attached between two adjacent battery cells, including a first electrode plate and a second electrode plate. The first electrode plate is attached to the side surface of the first battery cell, and the second electrode plate is attached to the side surface of the adjacent second battery cell. The first electrode plate and the second electrode plate are arranged opposite to each other to form a parallel plate capacitor structure. When either battery cell experiences the early stage of thermal runaway, the internal gas generation causes the casing to bulge outward, resulting in displacement of the side surface of the battery cell. This displacement causes the electrode plate to move, thereby changing the distance between the first electrode plate and the second electrode plate, resulting in a change in capacitance value, thus achieving non-contact measurement of battery deformation. The sensor is connected to two flexible leads by conductive adhesive, which are led out from the first electrode plate and the second electrode plate respectively, for outputting deformation signals.

[0007] The battery internal temperature monitoring device is located inside the cell, between the separator and the negative electrode, and includes a three-layer step temperature sensor. This sensor consists of a first thermochromic material layer, a second thermochromic material layer, and a third thermochromic material layer, arranged concentrically in the same plane. The third thermochromic material layer is located in the central circular region, and its phase transition temperature corresponds to the internal short-circuit stage during thermal runaway. The second thermochromic material layer surrounds the first thermochromic material layer in a ring shape, and its phase transition temperature corresponds to the separator melting stage during thermal runaway. The first thermochromic material layer surrounds the second thermochromic layer in a ring shape, and its phase transition temperature corresponds to the SEI film decomposition stage in the early stage of thermal runaway.

[0008] Each thermochromic material layer is composed of a thermochromic material body and extends outward to form two independent leads. A metal electrode is located at the end of each lead for connecting to an external detection circuit. When the internal temperature of the cell reaches the phase transition temperature of a certain thermochromic material layer, that layer changes from an insulating state to a conductive state. Its body region and the two leads simultaneously become conductive, forming a low-resistance path between the two corresponding metal electrodes, outputting a step signal at that temperature node.

[0009] The pressure relief valve membrane pressure sensor is located on the outside of the battery pressure relief valve and includes an annular base, a sealing ring, an annular lower electrode, a porous conductive foam layer, a mesh upper electrode, and a waterproof and breathable protective membrane. An air inlet is located at the center of the pressure relief valve top cover, and the annular base is pressed against the battery top cover by the sealing ring. The annular lower electrode is located on the upper surface of the annular base, forming an annular structure with a central opening. The porous conductive foam layer is located above the annular lower electrode and is made of a composite porous foam material of graphite nanosheets and polydimethylsiloxane, prepared using a granule template method to form an interconnected porous structure. Preferably, the graphite nanosheets have a mass percentage of 4.2%-4.8%. The mesh upper electrode is located above the porous conductive foam layer and has a porous and breathable structure. The waterproof and breathable protective membrane covers the mesh upper electrode, with its edges sealed to the annular base. The pressure relief valve has an opening pressure threshold of 2.0-3.5 MPa. The thin-film pressure sensor uses a composite porous foam of graphite nanosheets and polydimethylsiloxane as the porous conductive foam layer material, setting its resistance jump threshold to 1.5-2.0 MPa, slightly lower than the lower limit of the pressure relief valve's opening pressure. When the internal pressure of the battery rises to near the pressure relief valve's opening value, high-pressure gas impacts the porous conductive foam layer through the air inlet of the base and the empty area in the center of the annular lower electrode, causing it to compress and deform, the internal pore structure to collapse, the conductive network to break, and the resistance to jump by an order of magnitude (≥1MΩ). This outputs a switch-type pressure trigger signal, achieving an early warning before the pressure relief valve opens. The pressure relief valve then opens to release pressure. If the porous conductive foam layer of the sensor reaches the threshold and breaks at the moment the pressure relief valve opens, an alarm is triggered.

[0010] All leads of the capacitive displacement sensor, the three-layer step temperature sensor, and the pressure relief valve diaphragm pressure sensor converge at the flexible circuit board or terminal block on the top of the battery cover, and are connected to the external signal acquisition and processing unit via connectors; each sensor is led out independently and does not interfere with each other. The signal acquisition and processing unit includes multiple pull-up resistors and filter capacitors, used to convert the output signals of each sensor into logic level signals and filter out high-frequency interference.

[0011] The thermal runaway graded alarm unit includes a logic judgment unit, an isolation drive unit, and an indication unit.

[0012] The logic judgment unit consists of an inverter, multiple AND gates, a square wave oscillator, and an OR gate. The deformation signal output from the capacitive displacement sensor is connected to the first four-input AND gate and the second three-input AND gate, respectively. The 85℃ signal is inverted and then connected to the first four-input AND gate; the 135℃ signal is directly connected to the first four-input AND gate (as the original signal) and inverted and then connected to the second three-input AND gate; the air pressure signal is inverted and then connected to the first four-input AND gate and the second three-input AND gate, while the original air pressure signal is directly connected to the third two-input AND gate; the 200℃ signal is directly connected to the third two-input AND gate.

[0013] To identify operating conditions where the temperature is between 135℃ and 200℃ and triggered by air pressure, a square wave oscillator, along with additional AND and OR gates, are added. The original air pressure signal is ANDed with the inverted 135℃ signal to obtain the flashing enable signal; then, the output of the square wave oscillator is ANDed with this enable signal to obtain the flashing signal. The secondary alarm signal output from the second and third input AND gates is combined with the flashing signal via an OR gate to serve as the orange light drive signal.

[0014] The output logic is as follows: The first four-input AND gate outputs a level one warning signal, provided that the deformation signal, the 85°C inverted signal, the 135°C original signal, and the air pressure inverted signal are all high simultaneously. The second three-input AND gate outputs a level two alarm signal, provided that the deformation signal, the 135°C inverted signal, and the air pressure inverted signal are all high simultaneously. An OR gate outputs a severe warning signal, provided that the air pressure original signal and the 135°C inverted signal are both high simultaneously, displaying a flashing square wave. The third two-input AND gate outputs a level three alarm signal, provided that the 200°C signal and the air pressure original signal are both high simultaneously. These four alarm signals are mutually exclusive; at any given time, only one signal is active, ensuring that the indicator unit always displays the highest current risk level.

[0015] The isolation drive unit includes four optocouplers, each receiving one of the four alarm signals to achieve electrical isolation between the low-voltage circuit on the sensor side and the indicator side circuit. The indicator unit includes a yellow LED, an orange LED, and a red LED. The yellow LED corresponds to a level one warning, the red LED to a level three alarm, and the orange LED is shared by the level two alarm and the critical warning: it remains lit when the level two alarm is active, flashes at a square wave frequency when the critical warning is active, and turns off when both signals are inactive. The anode of each LED is connected to the output terminal of the corresponding optocoupler, and the cathode is grounded.

[0016] The technical solution of this invention to solve the aforementioned technical problem is to provide a control method for a multi-level early warning system for battery thermal runaway that integrates a capacitor displacement sensor, a battery internal temperature monitoring device, and a pressure relief valve diaphragm pressure sensor. The method is characterized by the following steps:

[0017] Step 1: Start the energy storage battery monitoring system.

[0018] Step 2: The signal acquisition and processing unit acquires in real time the battery casing deformation signal output by the capacitive displacement sensor, the step signals of three temperature nodes (85℃, 135℃, and 200℃) output by the battery internal temperature monitoring device, and the air pressure jump signal output by the pressure relief valve diaphragm pressure sensor, and transmits each signal to the logic judgment unit.

[0019] Step 3: The logic judgment unit combines and judges multiple signals according to preset priorities. The priorities from high to low are: Level 3 alarm, critical warning, Level 2 warning, and Level 1 early warning.

[0020] Step 4: If the pressure relief valve diaphragm pressure sensor outputs a trigger signal and the third temperature-changing material layer outputs a 200°C trigger signal, then a level 3 alarm is determined to have occurred, corresponding to the thermal runaway outbreak period. At the same time, a level 3 alarm signal is output, and all other alarm signals are blocked.

[0021] Step 5: If the Level 3 alarm is not triggered, and the pressure relief valve diaphragm pressure sensor outputs a trigger signal and the second temperature-changing material layer outputs a 135°C trigger signal, then a serious warning is determined to have occurred, corresponding to the middle stage of thermal runaway and the abnormal air pressure stage. A square wave flashing signal is output to drive the orange LED to flash, while the Level 2 warning and Level 1 early warning signals are blocked.

[0022] Step 6: If neither the Level 3 alarm nor the critical warning is triggered, and the capacitive displacement sensor outputs a deformation trigger signal, the second temperature change material layer outputs a 135°C trigger signal, and the pressure relief valve diaphragm pressure sensor does not output a trigger signal, then a Level 2 warning is determined to have occurred. This corresponds to the diaphragm melting stage during thermal runaway. A Level 2 alarm signal is output to drive the orange LED to remain constantly lit, while simultaneously blocking the Level 1 warning signal.

[0023] Step 7: If the Level 3 alarm, critical warning and Level 2 warning are not triggered, and the capacitive displacement sensor outputs a deformation trigger signal, the first temperature change material layer outputs an 85°C trigger signal and the pressure relief valve diaphragm pressure sensor does not output a trigger signal, then a Level 1 warning is determined to have occurred, corresponding to the initial stage of thermal runaway, and a Level 1 alarm signal is output, and the yellow LED is lit.

[0024] Step 8: The alarm signals output by the logic judgment unit are transmitted to the indicator unit via the isolation drive unit. The indicator unit illuminates the corresponding colored LED indicator according to the received alarm signal level: a yellow LED illuminates for a level 1 warning, a solid orange LED for a level 2 warning, a flashing orange LED for a level 3 warning, and a red LED for a level 3 alarm. Only one LED can be illuminated at any given time to ensure that the highest current risk level is displayed.

[0025] Step 9: When the indicator unit lights up the red LED, it indicates that the battery has experienced thermal runaway and the battery circuit must be immediately cut off and the fire suppression system activated. When the orange LED lights up and is flashing, it indicates that the battery is in a high-risk state, with abnormal air pressure but the temperature has not yet reached 200°C. Monitoring should be intensified immediately and emergency measures should be prepared. When the orange LED lights up and is constantly lit, it indicates that the battery is in a medium-risk state, with the temperature reaching 135°C but the air pressure is normal. Monitoring should be intensified. When the yellow LED lights up, it indicates that the battery has experienced an early abnormality and maintenance and inspection should be arranged.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) Integrating the capacitive displacement sensor, the three-layer step temperature sensor and the pressure relief valve membrane pressure sensor into the same early warning system makes full use of the high sensitivity of the capacitive displacement sensor to the expansion deformation of the battery casing, the step response characteristics of the three-layer step temperature sensor to the key temperature nodes of thermal runaway, and the rapid capture capability of the pressure relief valve membrane pressure sensor to the sudden pressure jump at the moment the pressure relief valve is opened. It can take into account the deformation perception in the early stage of thermal runaway, the temperature graded early warning in the middle stage, and the pressure confirmation in the later stage. In terms of comprehensive monitoring performance, it is superior to the existing single sensor early warning technology.

[0028] (2) The system integrates multi-parameter fusion sensing and hardware logic hierarchical judgment scheme. The capacitive displacement sensor monitors the shell bulging deformation in real time. The three-layer step temperature sensor corresponds to the three key thermal runaway temperature nodes of 85℃, 135℃ and 200℃ respectively. The pressure relief valve diaphragm pressure sensor provides the final confirmation signal. The logic circuit composed of NOT gate and AND gate realizes multi-level alarm output, comprehensively senses the evolution process of battery thermal runaway and reduces the false alarm rate.

[0029] (3) The system takes into account the reliable transmission of sensor signals in complex electromagnetic environments and designs an optocoupler isolation drive unit to realize the electrical isolation between the low-voltage circuit on the sensor side and the alarm indication circuit, thus ensuring the reliability and safety of the system in the high-voltage battery environment.

[0030] (4) The system integrates a three-color LED indicator hierarchical alarm device. The yellow LED, orange LED and red LED correspond to the first-level warning, second-level warning and third-level alarm of thermal runaway, respectively. It can intuitively display the different stages of thermal runaway and provide clear battery status indication for operation and maintenance personnel. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the adjacent battery cell structure and sensor arrangement of the present invention.

[0032] Figure 2 This is a schematic diagram of the diaphragm pressure sensor structure of the pressure relief valve of the present invention.

[0033] Figure 3 This is a cross-sectional view of the internal structure of the battery cell of the present invention.

[0034] Figure 4 This is a schematic diagram of the three-layer step temperature sensor structure of the present invention.

[0035] Figure 5 This is a schematic diagram of the arrangement of the three-layer step temperature sensor of the present invention.

[0036] Figure 6 This is a schematic diagram of the arrangement of the capacitive displacement sensor of the present invention.

[0037] Figure 7 This is the circuit alarm diagram for the present invention.

[0038] Figure 8 This is the control flowchart of the present invention.

[0039] In the diagram: 10. Overall cell structure; 100. Positive electrode; 101. Separator; 102. Negative electrode; 103. Cell stacking section; 11. Battery terminals; 12. Battery casing.

[0040] 20. The entire three-layer step temperature sensor consists of: 201, first thermochromic material layer; 202, second thermochromic material layer; 203, third thermochromic material; and 204, electrodes.

[0041] 30. Pressure relief valve diaphragm pressure sensor assembly; 301. Waterproof and breathable protective membrane; 302. Mesh upper electrode; 303. Porous conductive foam layer; 304. Annular lower electrode; 305. Annular base; 306. Sealing ring.

[0042] 40. Capacitive displacement sensor. Detailed Implementation

[0043] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the claims of the present invention.

[0044] This invention provides a multi-level early warning system for battery thermal runaway that integrates a capacitive displacement sensor, a battery internal temperature monitoring device, and a pressure relief valve diaphragm pressure sensor. The system includes a capacitive displacement sensor assembly 40, a three-layer step temperature sensor assembly 20, a pressure relief valve diaphragm pressure sensor assembly 30, a signal acquisition and processing unit, a logic judgment unit, an isolation drive unit, and an indication unit.

[0045] The capacitive displacement sensor 40 is attached between two adjacent battery cells, including a first electrode plate and a second electrode plate, which are respectively attached to the side surfaces of the two adjacent battery cells and arranged opposite each other to form a parallel plate capacitor structure. When any battery cell experiences bulging deformation of the casing in the early stage of thermal runaway, the side surface of the battery cell is displaced, causing the electrode plates to move, changing the distance between the two electrode plates, and the capacitance value changes accordingly, realizing non-contact measurement of battery expansion deformation. The sensor outputs deformation signals through two flexible leads.

[0046] The battery internal temperature monitoring device includes a three-layer stepped temperature sensor assembly 20 disposed inside the battery cell, located between the separator 101 and the negative electrode 102. The three-layer stepped temperature sensor assembly 20 is composed of a first thermochromic material layer 201, a second thermochromic material layer 202, and a third thermochromic material layer 203, which are arranged concentrically in the same plane. The third thermochromic material layer is located in the central circular region and is made of a tin-silver-copper composite alloy particle containing a tin-zinc low-melting phase and a modified polyimide matrix composite material. The composite alloy particle includes a tin-silver-copper alloy core and a tin-zinc low-melting phase coated or dispersed on the surface of the tin-silver-copper alloy core. The tin-silver-copper alloy core contains, by mass percentage: 95%-97% tin, 3%-4% silver, and 0.5%-1.0% copper. The tin-zinc low-melting phase contains, by mass percentage: 89%-92% tin and 8%-10% zinc, with a melting point of 198°C-202°C. The mass ratio of the tin-silver-copper alloy core to the tin-zinc low-melting phase is 50-70:30-50. The mass ratio of the composite alloy particles to the modified polyimide matrix is ​​approximately 7:3; the phase transition temperature of this layer is 200±5℃, corresponding to the internal short-circuit stage during the thermal runaway outbreak; the modified polyimide matrix includes polyimide, heat-softening resin, and wetting agent, with a mass ratio of 60-80:15-35:2-8, preferably 70:25:5; the heat-softening resin softens or loses its stickiness in the range of 190°C-205°C, and the wetting agent is activated near 200°C and promotes the wetting of the metal particles and metal electrode by the molten tin-zinc low-melting phase. At room temperature and below 195°C, the composite alloy particles are isolated by the modified polyimide matrix, and the third thermochromic material layer is in a high-resistance insulating state. When the temperature reaches 200±5°C, the tin-zinc low-melting phase melts, the thermal softening resin softens or loses its adhesion, the wetting agent is activated, and the molten tin-zinc low-melting phase connects adjacent tin-silver-copper alloy particles and wets the metal electrodes, thereby forming a continuous and stable low-resistance metal path between the metal electrodes. This causes the third thermochromic material layer to transition from an insulating state to a conductive state, and outputs a step electrical signal corresponding to the internal short-circuit stage during the thermal runaway outbreak. The second thermochromic material layer surrounds the third thermochromic material layer in a ring shape, using a tin-bismuth eutectic alloy and an epoxy resin matrix composite. The composite material consists of a tin-bismuth alloy comprising, by mass percentage: 40%-43% tin and 57%-60% bismuth, with a mass ratio of the alloy to the epoxy resin matrix of approximately 5:5; the phase transition temperature of this layer is 135±5℃, corresponding to the membrane melting stage during the middle of thermal runaway; the first thermochromic material layer is annularly surrounding the outside of the second thermochromic material layer, and is a composite material of indium-tin low-melting-point alloy and polyurethane matrix, wherein the bismuth-indium-tin alloy comprises, by mass percentage: 32%-35% bismuth, 48%-52% indium, with the balance being tin, with a mass ratio of the alloy to the polyurethane matrix of approximately 4:6; the phase transition temperature of this layer is 85±5℃, corresponding to the SEI film decomposition stage in the early stage of thermal runaway.Each thermochromic material layer extends outward to form two independent leads, each with a metal electrode 204 for independent connection to an external detection circuit. At room temperature, the alloy particles in each thermochromic material layer are encapsulated by an insulating substrate, and the electrodes are in a high-blocking open state. When the internal temperature of the cell reaches the melting point of the corresponding alloy, the thermochromic material layer changes from an insulating state to a conductive state, and its main body and the two leads simultaneously become conductive, forming a low-resistance path between the two corresponding metal electrodes, outputting a step signal at that temperature node. Each lead is connected to a metal electrode 204 via ultrasonic welding or conductive adhesive and is connected to a flexible lead wire for outputting step signals at three temperature nodes: 85℃, 135℃, and 200℃.

[0047] The pressure relief valve diaphragm pressure sensor assembly 30 is disposed on the outside of the battery pressure relief valve, and includes an annular base 305, a sealing ring 306, an annular lower electrode 304, a porous conductive foam layer 303, a mesh upper electrode 302, and a waterproof and breathable protective membrane 301. The annular base 305 has an air inlet at its center, directly opposite the pressure relief valve. The annular base 305 is pressed against the battery top cover by the sealing ring 306, with the air inlet directly opposite the pressure relief valve. The annular lower electrode 304 is disposed on the upper surface of the annular base 305, forming an annular structure with a central opening. The porous conductive foam layer 303 is disposed above the annular lower electrode 304, and is made of a composite porous foam material of graphite nanosheets and polydimethylsiloxane, prepared using a granule template method to form an interconnected porous structure. Preferably, the graphite nanosheets have a mass percentage of 4.2%-4.8%. The mesh upper electrode 302 is disposed above the porous conductive foam layer 303, forming a porous and breathable structure. A waterproof and breathable protective membrane 301 covers the mesh upper electrode 302, and its edges are sealed to the annular base 305. Under normal conditions, the graphite conductive network inside the porous conductive foam layer 303 is connected, and the resistance between the annular lower electrode 304 and the mesh upper electrode 302 is in a low-resistance conductive state (≤2kΩ). When the pressure relief valve is opened, high-pressure gas impacts the porous conductive foam layer 303 through the air inlet, causing it to compress and deform, the internal pore structure collapses, the conductive network breaks, and the resistance jumps by an order of magnitude (≥1MΩ), outputting a switching gas pressure trigger signal. The annular lower electrode 304 and the mesh upper electrode 302 extend outward to form leads, and flexible leads are welded to the ends.

[0048] All leads of the capacitive displacement sensor 40, the three-layer step temperature sensor 20, and the pressure relief valve diaphragm pressure sensor 30 converge at the flexible circuit board or terminal block on the top cover of the battery, and are connected to an external signal acquisition and processing unit via connectors. Each sensor is led out independently and does not interfere with each other.

[0049] The signal acquisition and processing unit includes multiple pull-up resistors and filter capacitors, which are used to convert the output signals of each sensor into logic level signals and filter out high-frequency interference.

[0050] The logic judgment unit includes an inverter, multiple AND gates, a square wave oscillator, and an OR gate. The specific connection method is as follows:

[0051] The output of the capacitive displacement sensor serves as the deformation signal, connected to the first input of a 74HC21 four-input AND gate and the first input of a 74HC11 three-input AND gate, respectively. The 85℃ signal, after being inverted by an inverter, becomes an inverted 85℃ signal, connected to the second input of the 74HC21 four-input AND gate. The 135℃ signal is directly connected to the third input of the 74HC21 four-input AND gate, and after being inverted by an inverter, it becomes an inverted 135℃ signal, connected to the second input of the 74HC11 three-input AND gate. The air pressure signal, after being inverted by an inverter, becomes an inverted air pressure signal, connected to the fourth input of a 74HC21 four-input AND gate and the third input of a 74HC11 three-input AND gate; simultaneously, the original air pressure signal is directly connected to the first input of a 74HC08 two-input AND gate. The 200℃ signal, after being inverted, is connected to the second input of a 74HC08 two-input AND gate.

[0052] To handle the condition of air pressure triggering with temperatures between 135℃ and 200℃, a square wave oscillator NE555 with an output frequency of 2-5Hz and additional logic circuitry are added. The original air pressure signal and the inverted 135℃ signal are input into the first additional 74HC08 AND gate, which outputs the flashing enable signal FLASH_CTRL. The square wave output of the NE555 and the FLASH_CTRL signal are input into the second additional 74HC08 AND gate, which outputs the flashing signal. The secondary warning signal and the flashing signal output from the 74HC11 three-input AND gate are input into the 74HC32 OR gate, and the output of the OR gate is used as the driving signal for the orange LED.

[0053] The 74HC21 four-input AND gate outputs a level 1 warning signal, with the logic condition that the deformation signal, the inverted 85°C signal, the original 135°C signal, and the inverted air pressure signal are all high simultaneously. The 74HC11 three-input AND gate outputs a level 2 warning signal, with the logic condition that the deformation signal, the inverted 135°C signal, and the inverted air pressure signal are all high simultaneously. The second additional 74HC08 AND gate outputs a severe warning signal, with the logic condition that the original air pressure signal and the inverted 135°C signal are both high simultaneously, appearing as an alternating square wave high and low level signal. The 74HC08 two-input AND gate outputs a level 3 alarm signal, with the logic condition that the 200°C signal and the original air pressure signal are both high simultaneously. The level 1 warning, level 2 warning, severe warning, and level 3 alarm signals are mutually exclusive; at most one signal can be active at any given time. The severe warning causes the orange LED to flash, while the level 2 warning causes the orange LED to remain constantly lit, making them inherently mutually exclusive due to their opposite air pressure states.

[0054] The isolation drive unit includes three optocouplers, each receiving one of three alarm signals to achieve electrical isolation between the low-voltage circuit on the sensor side and the indicator side circuit. The indicator unit includes a yellow LED, an orange LED, and a red LED, corresponding to Level 1 warning, Level 2 warning, severe warning, and Level 3 alarm, respectively. The anode of each LED is connected to the output terminal of the corresponding optocoupler, and the cathode is grounded. When the Level 1 warning signal is triggered, the first optocoupler conducts, and the yellow LED illuminates, indicating the initial SEI film decomposition stage of thermal runaway. When the Level 2 warning signal is triggered, the second optocoupler conducts, and the orange LED remains constantly lit, indicating the membrane melting stage during thermal runaway. When the severe warning signal is triggered, the second optocoupler also conducts, but the drive signal is a square wave, and the orange LED flashes at a set frequency, indicating that the temperature has reached 135℃ but not yet 200℃ and the air pressure signal has been triggered. When the Level 3 alarm signal is triggered, the third optocoupler conducts, and the red LED illuminates, indicating the internal short circuit stage during the thermal runaway outbreak.

[0055] This invention also provides a control method for a multi-stage early warning system for battery thermal runaway that integrates a capacitive displacement sensor, a battery internal temperature monitoring device, and a pressure relief valve diaphragm pressure sensor. The method includes the following steps:

[0056] Step 1: The energy storage battery monitoring system is turned on and running. The capacitor displacement sensor, the three-layer step temperature sensor, and the pressure relief valve diaphragm pressure sensor begin real-time monitoring.

[0057] Step 2: The signal acquisition and processing unit acquires in real time the battery casing deformation signal output by the capacitive displacement sensor, the step signals of the three temperature nodes of 85℃, 135℃ and 200℃ output by the three-layer step temperature sensor, and the air pressure jump signal output by the pressure relief valve diaphragm pressure sensor, and transmits each signal to the logic judgment unit.

[0058] Step 3: The logic judgment unit combines and judges multiple signals according to preset priorities, with the priorities from high to low being three-level alarm, critical warning, two-level warning, and one-level early warning.

[0059] Step 4: If the pressure relief valve diaphragm pressure sensor outputs a trigger signal and the third temperature-changing material layer outputs a 200°C trigger signal, then a level 3 alarm is determined to have occurred. This corresponds to the thermal runaway outbreak period. A level 3 alarm signal is output, while all other alarm signals are blocked.

[0060] Step 5: If the Level 3 alarm is not triggered, and the pressure relief valve diaphragm pressure sensor outputs a trigger signal and the second temperature-changing material layer outputs a 135°C trigger signal, then a serious warning is determined to have occurred, corresponding to the middle stage of thermal runaway and the abnormal air pressure stage. A square wave flashing signal is output to drive the orange LED to flash, while the Level 2 warning and Level 1 early warning signals are blocked.

[0061] Step 6: If neither the Level 3 alarm nor the critical warning is triggered, and the capacitive displacement sensor outputs a deformation trigger signal, the second temperature change material layer outputs a 135°C trigger signal, and the pressure relief valve diaphragm pressure sensor does not output a trigger signal, then a Level 2 warning is determined to have occurred. This corresponds to the diaphragm melting stage during thermal runaway. A Level 2 alarm signal is output to drive the orange LED to remain constantly lit, while the Level 1 warning signal is blocked.

[0062] Step 7: If the Level 3 alarm, critical warning and Level 2 warning are not triggered, and the capacitive displacement sensor outputs a deformation trigger signal, the first temperature change material layer outputs an 85°C trigger signal and the pressure relief valve diaphragm pressure sensor does not output a trigger signal, then a Level 1 warning is determined to have occurred, corresponding to the initial stage of thermal runaway, and a Level 1 alarm signal is output, illuminating the yellow LED.

[0063] Step 8: The alarm signals output by the logic judgment unit are transmitted to the indicator unit via the isolation drive unit. The indicator unit illuminates the corresponding colored LED indicator according to the received alarm signal level: a yellow LED illuminates for a level 1 warning, a solid orange LED for a level 2 warning, a flashing orange LED for a level 3 warning, and a red LED for a level 3 alarm. Only one LED can be lit at any given time, ensuring that the highest current risk level is displayed.

[0064] Step 9: When the indicator unit lights up the red LED, it indicates that the battery has experienced thermal runaway and the battery circuit must be immediately disconnected and the fire suppression system activated. When the orange LED lights up and is flashing, it indicates that the battery is in a high-risk state (abnormal air pressure but temperature has not yet reached 200°C), and monitoring must be intensified immediately and emergency measures prepared. When the orange LED lights up and is constantly lit, it indicates that the battery is in a medium-risk state (temperature has reached 135°C but air pressure is normal), and monitoring must be intensified. When the yellow LED lights up, it indicates that the battery has experienced an early abnormality, and maintenance and inspection must be arranged.

[0065] Any aspects not covered in this invention are applicable to existing technologies.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-stage early warning device for battery thermal runaway, characterized in that: The device includes a capacitive displacement sensor, a three-layer step temperature sensor, a pressure relief valve diaphragm pressure sensor, a signal acquisition and processing unit, a logic judgment unit, an isolation drive unit, and an indication unit. The capacitive displacement sensor includes a first electrode plate and a second electrode plate, which are respectively attached to the side surfaces of two adjacent cells and arranged opposite to each other to form a parallel plate capacitor structure; the two electrode plates output deformation signals through flexible leads; The three-layer step temperature sensor is installed inside the battery cell for monitoring the internal temperature of the battery. The three-layer step temperature sensor includes a first temperature-changing material layer, a second temperature-changing material layer, and a third temperature-changing material layer, which are arranged concentrically in the same plane. Each temperature-changing material layer extends outward to form two independent leads, and the ends of the leads are provided with metal electrodes for independently connecting to external detection circuits and outputting step signals at three temperature nodes of 85°C, 135°C, and 200°C respectively. The pressure sensor of the pressure relief valve is located on the outside of the battery pressure relief valve. The annular lower electrode and the mesh upper electrode extend outward to form lead-out ends, and flexible leads are welded to the ends to output air pressure signals. All leads of the capacitive displacement sensor, the three-layer step temperature sensor, and the pressure relief valve diaphragm pressure sensor converge at the flexible circuit board or terminal block at the top of the battery, and are connected to the external signal acquisition and processing unit through connectors. The signal acquisition and processing unit includes multiple pull-up resistors and filter capacitors, which are used to convert the output signals of each sensor into logic level signals. The logic judgment unit includes an inverter, several AND gates, a square wave oscillator, and an OR gate; the logic judgment unit is configured to receive deformation signals, 85°C signals, 135°C signals, 200°C signals, and air pressure signals, and output yellow light drive signals, red light drive signals, and orange light drive signals respectively according to the logical combination of each signal. The yellow light driving signal is output from a four-input AND gate and then drives the yellow light via an optocoupler; the red light driving signal is output from a first two-input AND gate and then drives the red light via an optocoupler; and the orange light driving signal is output from an OR gate and then drives the orange light via an optocoupler. The inputs of the four-input AND gate include the deformation signal, the inverted signal of the 85°C signal, the 135°C signal, and the inverted signal of the air pressure signal. The inputs of the first two-input AND gate include the inverted signal of the 200°C signal and the air pressure signal; The inputs of the OR gate include: a secondary warning signal output from a three-input AND gate, and a flashing signal obtained by controlling a square wave signal output from a square wave oscillator through a second two-input AND gate; The inputs of the three-input AND gate include the deformation signal, the inverted signal of the 135°C signal, and the inverted signal of the air pressure signal. The second two-input AND gate is enabled by the output signal of the first additional two-input AND gate. The inputs of the first additional two-input AND gate are the inverted signal of the 135°C signal and the air pressure signal. The isolation drive unit includes three optocouplers, which receive three alarm signals respectively, to achieve electrical isolation between the low-voltage circuit on the sensor side and the indicator side circuit. The indicator unit includes a yellow LED, an orange LED, and a red LED. The yellow LED corresponds to the first-level warning, the red LED corresponds to the third-level alarm, and the orange LED is shared by the second-level alarm and the critical warning: it is always on when the second-level alarm is valid, it flashes at a square wave frequency when the critical warning is valid, and it is off when both signals are invalid. The anode of each LED is connected to the output terminal of the corresponding optocoupler, and the cathode is grounded.

2. The multi-stage early warning device for battery thermal runaway according to claim 1, characterized in that: In the capacitive displacement sensor, when the battery cell to which any two plates are attached experiences a bulging deformation of the casing in the early stage of thermal runaway, the side surface of the battery cell is displaced, which drives the plates to move, changes the distance between the two plates, and the capacitance value changes accordingly, thus realizing non-contact measurement of battery expansion deformation.

3. The multi-stage early warning device for battery thermal runaway according to claim 1, characterized in that: The third thermochromic material layer is located in the central circular region and is made of tin-silver-copper composite alloy particles containing tin-zinc low-melting phase and modified polyimide matrix composite material. Its phase transition temperature is 200℃±5℃, corresponding to the internal short circuit stage during the thermal runaway outbreak. The second thermochromic material layer is annularly surrounding the outside of the first thermochromic material layer and is made of tin-bismuth eutectic alloy and epoxy resin matrix composite material. Its phase transition temperature is 135℃±5℃, corresponding to the membrane melting stage during the thermal runaway. The third thermochromic material layer is annularly surrounding the outside of the second thermochromic material layer and is made of indium-tin alloy and polyurethane matrix composite material. Its phase transition temperature is 85℃±5℃, corresponding to the SEI film decomposition stage in the early stage of thermal runaway.

4. The multi-stage early warning device for battery thermal runaway according to claim 3, characterized in that: At room temperature, the alloy particles in each temperature-sensitive material layer are wrapped by an insulating matrix, and the electrodes are in a high-blocking open state. When the internal temperature of the cell reaches the melting point of the corresponding alloy, the temperature-sensitive material of the corresponding layer changes from an insulating state to a conductive state, and its body area and two leads are simultaneously connected. A low-resistance path is formed between the two corresponding metal electrodes, and the step signal of that temperature node is output.

5. A multi-stage early warning device for battery thermal runaway according to claim 1, characterized in that: The pressure relief valve diaphragm pressure sensor includes an annular base, a sealing ring, an annular lower electrode, a porous conductive foam layer, a mesh upper electrode, and a waterproof and breathable protective membrane. The annular base has an air inlet at its center, directly opposite the pressure relief valve. The annular base is pressed against the battery top cover by the sealing ring, with the air inlet directly facing the pressure relief valve. The annular lower electrode is located on the upper surface of the annular base, forming a ring structure with a central opening. The porous conductive foam layer is positioned above the annular lower electrode. The mesh upper electrode is positioned above the porous conductive foam layer, forming a porous and breathable structure. The waterproof and breathable protective membrane covers the mesh upper electrode, with its edges sealed to the annular base.

6. The multi-stage early warning device for battery thermal runaway according to claim 5, characterized in that: The porous conductive foam layer is made of graphite nanosheets and polydimethylsiloxane composite porous foam material, and the interconnected porous structure is prepared by granule template method; wherein, the graphite nanosheets account for 4.2%-4.8% of the mass percentage of the porous conductive foam layer.

7. A multi-stage early warning device for battery thermal runaway according to claim 6, characterized in that: Under normal pressure, the graphite conductive network inside the porous conductive foam layer is connected, and the resistance between the annular lower electrode and the mesh upper electrode is ≤2kΩ, exhibiting a low-resistance conductive state. When the pressure relief valve is opened, the high-pressure gas impacts the porous conductive foam layer through the air inlet, causing it to compress and deform, resulting in the collapse of the internal pore structure and the breakage of the conductive network. The resistance is ≥1MΩ, and a gas pressure signal is output to trigger the switch quantity.

8. The multi-stage early warning device for battery thermal runaway according to claim 1, characterized in that: The specific connection method of the logic unit is as follows: The output of the capacitive displacement sensor serves as a deformation signal; the output of the three-layer step temperature sensor outputs 85℃, 135℃, and 200℃ signals; and the output of the pressure relief valve diaphragm pressure sensor serves as a gas pressure signal. The deformation signal is connected to the first input terminal of the 74HC21 four-input AND gate and the first input terminal of the 74HC11 three-input AND gate, respectively. The 85°C signal is inverted by an inverter to obtain an inverted 85°C signal, which is then connected to the second input of a 74HC21 quad-input AND gate. The 135°C signal is directly connected to the third input terminal of the 74HC21 four-input AND gate, and after being inverted by an inverter, the 135°C inverted signal is connected to the second input terminal of the 74HC11 three-input AND gate. The air pressure signal is directly connected to the first input terminal of the 74HC08 two-input AND gate; the 200℃ signal is inverted and connected to the second input terminal of the 74HC08 two-input AND gate; the air pressure signal is inverted by an inverter to obtain an inverted air pressure signal, which is connected to the fourth input terminal of the 74HC21 four-input AND gate and the third input terminal of the 74HC11 three-input AND gate, respectively. The air pressure signal and the 135℃ inverted signal are input into the first additional 74HC08 AND gate, which outputs the flashing enable signal FLASH_CTRL; the NE555 square wave output and the FLASH_CTRL signal are input into the second additional 74HC08 AND gate, which outputs the flashing signal; the secondary warning signal and the flashing signal output from the 74HC11 three-input AND gate are input into the 74HC32 OR gate, and the output of the OR gate is used as the orange LED driving signal; The output of the 74HC21 four-input AND gate outputs a first-level warning signal, the logic condition of which is that the deformation signal, the 85℃ inverted signal, the 135℃ original signal and the air pressure inverted signal are all high at the same time. The 74HC11 three-input AND gate outputs a two-level warning signal, the logic condition of which is that the deformation signal, the 135℃ inverted signal and the air pressure inverted signal are all high at the same time. The output of the second additional 74HC08 AND gate outputs a critical warning signal. Its logic condition is that the original air pressure signal and the 135℃ inverted signal are both high level at the same time, which is manifested as a square wave high and low level interleaved signal. The 74HC08 two-input AND gate outputs a three-level alarm signal, with the logic condition that the 200℃ signal and the original air pressure signal are both high.

9. A multi-stage early warning device for battery thermal runaway according to claim 1, characterized in that: When a Level 1 warning signal is triggered, the first optocoupler conducts, and the yellow LED lights up, indicating the initial stage of SEI film decomposition during thermal runaway. When a Level 2 warning signal is triggered, the second optocoupler conducts, and the orange LED remains lit, indicating the diaphragm melting stage during thermal runaway and that the pressure signal has not been triggered. When a severe warning signal is triggered, the second optocoupler also conducts, but the drive signal is a square wave, and the orange LED flashes at a set frequency, indicating that the temperature has reached 135°C but not yet 200°C and the pressure signal has been triggered. When a Level 3 alarm signal is triggered, the third optocoupler conducts, and the red LED lights up, indicating the internal short circuit stage during the thermal runaway outbreak.

10. A control method for a multi-stage early warning device for battery thermal runaway according to any one of claims 1-9, characterized in that, The method includes the following steps: Step 1: The energy storage battery monitoring system is turned on and running. The capacitor displacement sensor, the three-layer step temperature sensor, and the pressure relief valve diaphragm pressure sensor begin real-time monitoring. Step 2: The signal acquisition and processing unit acquires the battery casing deformation signal output by the capacitive displacement sensor, the step signals of the three temperature nodes of 85℃, 135℃ and 200℃ output by the three-layer step temperature sensor, and the air pressure jump signal output by the pressure relief valve diaphragm pressure sensor in real time, and transmits each signal to the logic judgment unit. Step 3: The logic judgment unit combines and judges multiple signals according to preset priorities. The priorities from high to low are: Level 3 alarm, critical warning, Level 2 warning, and Level 1 early warning. Step 4: If the pressure relief valve diaphragm pressure sensor outputs a trigger signal and the third temperature-changing material layer outputs a 200°C trigger signal, then a level 3 alarm is determined to have occurred, corresponding to the thermal runaway outbreak period. At the same time, a level 3 alarm signal is output, and all other alarm signals are blocked. Step 5: If the level 3 alarm is not triggered, and the pressure relief valve diaphragm pressure sensor outputs a trigger signal and the second temperature change material layer outputs a 135°C trigger signal, then a serious warning is determined to have occurred, corresponding to the middle stage of thermal runaway and the abnormal air pressure stage. A square wave flashing signal is output to drive the orange LED to flash, while the level 2 warning and level 1 early warning signals are blocked. Step 6: If neither the Level 3 alarm nor the critical warning is triggered, and the capacitive displacement sensor outputs a deformation signal, the second temperature change material layer outputs a 135°C trigger signal, and the pressure relief valve diaphragm pressure sensor does not output a trigger signal, then a Level 2 warning is determined to have occurred, corresponding to the diaphragm melting stage in the middle of thermal runaway. The Level 2 alarm signal is output to drive the orange LED to stay on, while the Level 1 warning signal is blocked. Step 7: If the Level 3 alarm, critical warning and Level 2 warning are not triggered, and the capacitive displacement sensor outputs a deformation signal, the first temperature change material layer outputs an 85°C trigger signal and the pressure relief valve diaphragm pressure sensor does not output a trigger signal, then it is determined that a Level 1 warning has occurred, corresponding to the initial stage of thermal runaway, and a Level 1 alarm signal is output and the yellow LED is lit. Step 8: The alarm signals output by the logic judgment unit are transmitted to the indicator unit via the isolation drive unit; the indicator unit lights up the corresponding colored LED indicator according to the received alarm signal level: a yellow LED lights up for a level 1 warning, a solid orange LED lights up for a level 2 warning, a flashing orange LED lights up for a level 3 alarm, and a red LED lights up for a level 3 alarm; at any given time, only one LED can be lit to ensure that the current highest risk level is displayed; Step 9: When the indicator unit lights up the red LED, it indicates that the battery has experienced thermal runaway and the battery circuit must be immediately disconnected and the fire suppression system activated; when the orange LED lights up and is flashing, it indicates that the battery is in a high-risk state and monitoring must be intensified immediately and emergency measures prepared; when the orange LED lights up and is constantly lit, it indicates that the battery is in a medium-risk state with the temperature reaching 135°C but the air pressure is normal and monitoring must be intensified; when the yellow LED lights up, it indicates that the battery has experienced an early abnormality and maintenance and inspection must be arranged.

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