A high-temperature self-adaptive micro-pump liquid cooling heat dissipation mobile power supply system and working method

Abstract

The application discloses a high-temperature self-adaptive micro-pump liquid cooling heat dissipation mobile power supply system and a working method, relates to the technical field of mobile energy storage power supply heat management, and comprises a shell, a lithium battery pack, a temperature acquisition unit, a main control unit, a micro-pump liquid cooling heat dissipation module, a charge and discharge management module and an over-temperature protection unit; the charge and discharge management module is electrically connected with the lithium battery pack and the main control unit; the temperature acquisition unit contains at least two temperature sensors and transmits temperature signals to the main control unit; the micro-pump liquid cooling heat dissipation module is a full-sealed closed loop circulation system, and comprises a piezoelectric micro-pump, a micro-channel liquid cooling plate, a circulation pipeline, insulating cooling liquid, a cooling liquid storage cavity and a heat dissipation fin group. The application adopts the high-temperature self-adaptive micro-pump liquid cooling heat dissipation mobile power supply system and the working method, realizes efficient, silent, accurate and stable temperature control of the lithium battery pack in a high-temperature environment, prolongs the service life of the battery, improves the use safety, and is suitable for various high-temperature mobile scenes.

Description

Technical Field

[0001] This invention relates to the field of thermal management technology for mobile energy storage power supplies, and in particular to a high-temperature adaptive micro-pump liquid cooling mobile power supply system and its operating method. Background Technology

[0002] Portable power banks, as portable energy storage devices, are widely used in emergency power supply scenarios for mobile phones, tablets, outdoor equipment, industrial instruments, and other devices. Their core component is the lithium battery pack. The performance of lithium batteries is closely related to temperature. When in high-temperature environments or during high-power charging and discharging, lithium battery packs rapidly generate a large amount of heat, causing the cell temperature to rise.

[0003] Current power banks primarily employ two heat dissipation methods: natural cooling and air cooling. Natural cooling relies on the casing's heat conduction, resulting in extremely low efficiency. In high-temperature environments, it cannot dissipate heat quickly enough, causing the battery cell temperature to rise continuously. Air cooling uses small fans to accelerate airflow, but its effectiveness is greatly affected by ambient temperature. Furthermore, the fans generate noise and consume significant power, and dust can easily enter the device, affecting its lifespan. In addition, traditional liquid cooling systems are bulky, complex in structure, and consume a lot of power, making them difficult to integrate into portable power banks and unsuitable for mobile usage scenarios.

[0004] In high-temperature environments, if lithium battery packs cannot effectively dissipate heat, a series of performance and safety issues will arise. In terms of performance, according to relevant test data, at 60℃, lithium batteries experience a 20-30% capacity drop within the first 50 cycles, and after 200 cycles, the capacity may stabilize below 50%, significantly shortening cycle life compared to room temperature. Simultaneously, high temperatures accelerate electrolyte decomposition and evaporation, leading to increased internal resistance and decreased charge / discharge performance. From a safety perspective, high temperatures damage the stability of the negative electrode SEI film, accelerating internal side reactions. When the temperature consistently exceeds 60℃, the degradation curve may suddenly terminate, potentially causing thermal runaway, leading to battery bulging, fire, or even explosion, posing a significant safety hazard. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature adaptive micro-pump liquid cooling mobile power supply system and its working method, so as to achieve efficient, quiet, precise and stable temperature control of lithium battery packs in high-temperature environments.

[0006] This invention provides a high-temperature adaptive micro-pump liquid-cooled mobile power supply system, including a housing, a lithium battery pack, a temperature acquisition unit, a main control unit, a micro-pump liquid-cooled heat dissipation module, a charge / discharge management module, and an over-temperature protection unit. The charge / discharge management module is electrically connected to the lithium battery pack and the main control unit. The temperature acquisition unit includes two temperature sensors and transmits temperature signals to the main control unit. The micro-pump liquid-cooled heat dissipation module is a fully sealed closed-loop circulation system, including a piezoelectric micro-pump, a microchannel liquid cooling plate, a circulation pipeline, an insulating coolant, a coolant storage chamber, a heat dissipation fin assembly, and a sealing ring. The microchannel liquid cooling plate is bonded to the surface of the lithium battery pack cells. The circulation pipeline sequentially connects the piezoelectric micro-pump, the microchannel liquid cooling plate, the heat dissipation fin assembly, and the coolant storage chamber to form a closed-loop circulation circuit. The main control unit is electrically connected to the temperature acquisition unit, the piezoelectric micro-pump, and the charge / discharge management module.

[0007] Preferably, the microchannel liquid cooling plate is integrally stamped from aluminum alloy or copper alloy, and the interior of the microchannel liquid cooling plate is provided with parallel microchannels, and the interface between the microchannels and the battery cell is filled with a thermally conductive interface material.

[0008] Preferably, the insulating coolant is an electronic fluorinated liquid or an aqueous solution of ethylene glycol.

[0009] Preferably, the piezoelectric micropump is an ultrathin piezoelectric ceramic driven micropump.

[0010] Preferably, the main control unit's graded temperature control program has three preset temperature thresholds and corresponding temperature control strategies.

[0011] Preferably, the over-temperature protection unit is connected in series with the main control unit and the charge / discharge management module.

[0012] Preferably, the housing is made of glass fiber reinforced PC / ABS alloy material.

[0013] A method for operating a high-temperature adaptive micro-pump liquid-cooled mobile power supply system includes the following steps: Step S1: Power-on self-test. After the system is powered on and started, the main control unit executes a self-test program to detect the working status of the temperature acquisition unit, piezoelectric micro-pump, charge and discharge management module, and over-temperature protection unit. After the self-test is passed, the system enters the normal working mode. Step S2: Real-time temperature acquisition. The temperature acquisition unit acquires the surface temperature of the lithium battery cell and the ambient temperature inside the casing in real time at a preset sampling frequency, and transmits the acquired temperature signal to the main control unit in real time. Step S3: Graded adaptive temperature control. The main control unit compares the real-time collected temperature data with the preset multi-level temperature thresholds, matches the corresponding temperature control strategy according to the temperature level, drives the piezoelectric micropump to adjust the coolant circulation flow rate, and realizes adaptive regulation of the cell temperature. Step S4: Multi-level safety protection. The main control unit monitors the system's operating status in real time. When the temperature reaches the current limiting protection threshold, it executes charging and discharging power limiting. When the temperature reaches the extreme over-temperature threshold, it triggers hardware-level over-temperature protection, cuts off the charging and discharging main circuit, and sends an alarm signal. After the temperature drops back to the safe range, the system automatically resumes normal operation.

[0014] Preferably, in step S3, the graded adaptive temperature control includes the following steps: Step S31: Under normal temperature and low load conditions, when the detected temperature is <45℃, the main control unit controls the piezoelectric micropump to be in a dormant state, and the system relies on the shell and heat dissipation fin assembly to achieve natural heat dissipation. Step S32, Temperature rise condition: When 45℃≤detection temperature<55℃, the main control unit outputs a PWM drive signal to control the piezoelectric micropump to operate at low flow rate, with the circulation flow rate stabilized at 30mL / min or above, and active heat dissipation is achieved through coolant circulation. Step S33, High temperature rise condition: When 55℃≤detection temperature<65℃, the main control unit increases the drive voltage to control the piezoelectric micropump to operate at high flow rate, and the circulation flow rate is stabilized at 50mL / min or above, thereby enhancing heat exchange efficiency and rapidly reducing the cell temperature. Step S34, Extreme Temperature Rise Condition: When the detected temperature is ≥65℃, the main control unit sends a current limiting command to the charge and discharge management module to reduce the charge and discharge current to 50% of the rated value. At the same time, it controls the piezoelectric micro pump to run continuously at high flow rate for strong cooling to suppress the cell temperature from rising further.

[0015] Therefore, the present invention adopts the above-mentioned high-temperature adaptive micro-pump liquid cooling heat dissipation mobile power supply system and working method to achieve efficient, quiet, precise and stable temperature control of lithium battery packs under high-temperature environments.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a block diagram of the overall system structure of a high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to the present invention. Figure 2 This is a structural block diagram of the micro-pump liquid cooling circuit of a high-temperature adaptive micro-pump liquid cooling mobile power supply system according to the present invention. Figure 3 This is a flowchart illustrating the working method of a high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to the present invention.

[0018] Figure Labels 1. Lithium battery pack; 2. Temperature acquisition unit; 3. Main control unit; 4. Temperature pump liquid cooling heat dissipation module; 41. Piezoelectric micropump; 42. Microchannel liquid cooling plate; 43. Circulation pipeline; 44. Coolant storage tank; 45. Heat dissipation fin assembly; 46. Sealing ring; 5. Charge and discharge management module; 6. Over-temperature protection unit. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] The terms "first," "second," and similar words used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0022] Example 1 like Figures 1-3 As shown, the present invention discloses a high-temperature adaptive micro-pump liquid cooling mobile power supply system, including a housing, a lithium battery pack 1, a temperature acquisition unit 2, a main control unit 3, a micro-pump liquid cooling module 4, a charge and discharge management module 5, and an over-temperature protection unit 6.

[0023] The housing is made of glass fiber reinforced PC / ABS alloy with a flame retardant rating of V0. It measures 120mm×60mm×20mm and features a rectangular dustproof ventilation grille measuring 80mm×10mm on the side. The top integrates a USB-A output port, a USB-C input / output port, a USB input port, a power indicator light, and control buttons.

[0024] The lithium battery pack 1 uses polymer ternary lithium cells, with a single cell capacity of 10Ah. Four cells are connected in series to form a 14.8V battery pack with a total capacity of 40Ah and a total power of 148W. A 1mm thick graphene thermal pad is attached to the surface of the cell. The graphene used in the thermal pad has a theoretical thermal conductivity of up to 5300W / mK. After attachment, it can effectively improve the heat conduction efficiency and ensure the thermal stability of the cell during operation.

[0025] The charge / discharge management module 5 is electrically connected to the lithium battery pack 1 and the main control unit 3, and is used to realize the charge / discharge control and circuit protection of the lithium battery pack 1. The charge / discharge management module 5 uses a fast charging chip to provide a complete power solution for the power bank. It has high charging efficiency and high boost efficiency, and has multiple protection functions such as overvoltage, overcurrent, overcharge, over-discharge, short circuit, and overall over-temperature protection. It also supports simultaneous charging and discharging, TFT screen display, and its high integration can effectively reduce the overall solution size and reduce BOM cost.

[0026] Temperature acquisition unit 2 includes at least two temperature sensors, which are respectively installed on the surface of the lithium battery cell and inside the casing, and transmit the temperature signals to the main control unit 3. Temperature acquisition unit 2 uses NTC thermistors of model MF52-103F-3950, with an accuracy of ±1℃ and an operating temperature range of -55℃–125℃. They are respectively attached to the surface of the cell and the inner wall of the casing, and connected to the main control unit 3 through wires.

[0027] Temperature acquisition unit 2 uses an STM32L431 microcontroller and employs FlexPowerControl to achieve ultra-low power consumption. It provides seven low-power modes, ranging from light sleep to deep shutdown. The power consumption in the operating mode ranges from approximately 27mA (full speed operation) to microamps, while the power consumption in the standby mode is approximately 2μA~5μA. Its operating voltage range is 1.71V-3.7V. It has a built-in 12-bit fast ADC module of 5Msps, which can directly receive electrical signals from temperature acquisition unit 2. The main control unit 3, which has a preset graded temperature control program, is electrically connected to temperature acquisition unit 2, piezoelectric micropump 41, and charge / discharge management module 5, respectively.

[0028] The main control unit 3 has a three-level temperature control program with preset temperature thresholds and corresponding temperature control strategies. When the detected temperature is less than 45℃, the piezoelectric micropump 41 is in a dormant state, and the system relies on the shell and heat sink fin assembly 45 for natural heat dissipation. When 45℃≤detected temperature<55℃, the main control unit 3 drives the piezoelectric micropump 41 to operate at a low flow rate, with a circulation flow rate ≥30mL / min. When 55℃≤detected temperature<65℃, the main control unit 3 drives the piezoelectric micropump 41 to operate at a high flow rate, with a circulation flow rate ≥50mL / min. When the detected temperature is ≥65℃, the main control unit 3 sends a current limiting command to the charge and discharge management module 5, reducing the charge and discharge current to 50% of the rated value, while the piezoelectric micropump 41 continues to operate at a high flow rate for strong cooling.

[0029] When the detected temperature reaches the first safety threshold, the main control unit 3 starts the piezoelectric micro pump 41, which drives the insulating coolant to flow in the closed-loop circulation circuit. The coolant exchanges heat with the lithium battery pack 1 through the microchannel liquid cooling plate 42, and then dissipates the heat to the external environment through the heat dissipation fin group 45, thereby realizing the adaptive regulation of the temperature of the lithium battery pack 1.

[0030] The micropump liquid cooling heat dissipation module is a fully sealed closed-loop circulation system. It includes a piezoelectric micropump 41, a microchannel liquid cooling plate 42, a circulation pipeline 43, insulating coolant, a coolant storage chamber 44, and a heat dissipation fin assembly 45. The microchannel liquid cooling plate 42 is bonded to the surface of the lithium battery cell 1. The circulation pipeline 43 sequentially connects the piezoelectric micropump 41, the microchannel liquid cooling plate 42, the heat dissipation fin assembly 45, and the coolant storage chamber to form a closed-loop circulation circuit. The joint of the circulation pipeline 43 adopts a double-seal structure, which includes a sealing ring 46 and sealant.

[0031] The piezoelectric micropump 41 used in the micropump liquid cooling heat dissipation module is model PZT-5H, with an operating voltage of 5V, power consumption of 0.3W, flow rate of 50mL / min, and dimensions of 20mm×20mm×5mm. This model of piezoelectric micropump 41 belongs to the category of piezoelectric micropumps, characterized by its small size, precise control, and low power consumption, making it particularly suitable for cooling systems of electronic equipment.

[0032] The microchannel liquid cooling plate 42 is made of one-piece aluminum alloy, 2mm thick, with 1mm parallel microchannels inside, and the surface is anodized. The insulating coolant is electronic fluorinated fluid model: 3MFC-72, which is insulating, high temperature resistant, and non-corrosive. The circulation pipe 43 uses high temperature resistant silicone tubing with a diameter of 4mm. The heat dissipation fin assembly 45 is made of anodized aluminum alloy, 1mm thick, with ten fins spaced 2mm apart.

[0033] The over-temperature protection unit 6 uses a KSD9700 temperature relay with an operating temperature of 70℃ and a reset temperature of 45℃. It is connected in series with the main control unit 3 and the charge / discharge management module 5 to realize the over-temperature cut-off circuit function. The over-temperature protection unit 6 is connected in series with the main control unit 3 and the charge / discharge management module 5. When the temperature acquisition unit 2 detects that the temperature of the lithium battery pack 1 is ≥70℃, the over-temperature protection unit 6 immediately cuts off the main charge / discharge circuit. At the same time, the main control unit 3 triggers an audible and visual alarm. After the temperature drops to 45℃ or below, the system automatically returns to normal operation.

[0034] A working method of a high-temperature adaptive micro-pump liquid cooling mobile power supply system includes the following steps: Step S1, power-on self-test: After the system is powered on and started, the main control unit 3 executes a self-test program to detect the working status of the temperature acquisition unit 2, the piezoelectric micro-pump 41, the charge and discharge management module 5, and the over-temperature protection unit 6. After the self-test is passed, the system enters the normal working mode.

[0035] Step S2: Real-time temperature acquisition. Temperature acquisition unit 2 acquires the surface temperature of the battery cells and the internal ambient temperature of the casing of lithium battery pack 1 in real time at a preset sampling frequency, and transmits the acquired temperature signals to the main control unit 3 in real time. In step S2, the sampling frequency of temperature acquisition unit 2 is ≥1Hz, and the temperature measurement accuracy is ≤±1℃.

[0036] Step S3: Graded adaptive temperature control. The main control unit 3 compares the real-time collected temperature data with preset multi-level temperature thresholds, matches the corresponding temperature control strategy according to the temperature level, and drives the piezoelectric micropump 41 to adjust the coolant circulation flow rate, thereby achieving adaptive regulation of the battery cell temperature. In step S3, the temperature control response time of the main control unit 3 is ≤2s, and the temperature difference of the battery cell operation is controlled within ±2℃.

[0037] In step S3, the graded adaptive temperature control includes the following steps: Step S31, normal temperature low load condition: when the detected temperature is <45℃, the main control unit 3 controls the piezoelectric micropump 41 to be in a dormant state, and the system relies on the shell and heat dissipation fin group 45 to achieve natural heat dissipation.

[0038] Step S32, Temperature rise condition: When 45℃≤detection temperature<55℃, the main control unit 3 outputs a PWM drive signal to control the piezoelectric micropump 41 to operate at low flow rate, with the circulation flow rate stabilized at 30mL / min or above, and active heat dissipation is achieved through coolant circulation.

[0039] Step S33, High Temperature Rise Condition: When 55℃≤Detection Temperature<65℃, the main control unit 3 increases the drive voltage to control the piezoelectric micropump 41 to operate at high flow rate, with the circulation flow rate stabilizing at 50mL / min or higher, thereby enhancing heat exchange efficiency and rapidly reducing the cell temperature.

[0040] Step S34, Extreme temperature rise condition: When the detected temperature is ≥65℃, the main control unit 3 sends a current limiting command to the charge and discharge management module 5 to reduce the charge and discharge current to 50% of the rated value. At the same time, it controls the piezoelectric micro pump 41 to run continuously at high flow rate for strong cooling to suppress the cell temperature from rising further.

[0041] Step S4: Multi-level safety protection. The main control unit 3 monitors the system's operating status in real time. When the temperature reaches the current limiting protection threshold, it implements charging and discharging power limitation. When the temperature reaches the extreme over-temperature threshold, it triggers hardware-level over-temperature protection, cutting off the main charging and discharging circuit and issuing an alarm signal. After the temperature drops back to the safe range, the system automatically resumes normal operation. In step S4, the extreme over-temperature threshold is set to 70℃, and the safe recovery threshold is set to 45℃. After the over-temperature protection is triggered, the system will only automatically resume normal charging and discharging functions if the cell temperature continues to drop to 45℃ or below and remains stable for more than 30 seconds.

[0042] Therefore, the present invention adopts the above-mentioned high-temperature adaptive micro-pump liquid cooling heat dissipation mobile power supply system and working method to achieve efficient, quiet, precise and stable temperature control of lithium battery packs in high-temperature environments, extend battery life, improve safety, and adapt to various high-temperature mobile scenarios.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-temperature adaptive micro-pump liquid-cooled mobile power supply system, characterized in that, The system includes a casing, a lithium battery pack, a temperature acquisition unit, a main control unit, a micro-pump liquid cooling module, a charge / discharge management module, and an over-temperature protection unit. The charge / discharge management module is electrically connected to the lithium battery pack and the main control unit. The temperature acquisition unit includes two temperature sensors that transmit temperature signals to the main control unit. The micro-pump liquid cooling module is a fully sealed closed-loop circulation system, comprising a piezoelectric micropump, a microchannel liquid cooling plate, circulation pipes, insulating coolant, a coolant reservoir, heat dissipation fins, and a sealing ring. The microchannel liquid cooling plate is bonded to the surface of the lithium battery cells. The circulation pipes sequentially connect the piezoelectric micropump, the microchannel liquid cooling plate, the heat dissipation fins, and the coolant reservoir to form a closed-loop circulation circuit. The main control unit is electrically connected to the temperature acquisition unit, the piezoelectric micropump, and the charge / discharge management module.

2. The high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to claim 1, characterized in that, The microchannel liquid cooling plate is integrally stamped from aluminum alloy or copper alloy. The interior of the microchannel liquid cooling plate is provided with parallel microchannels, and the interface between the microchannels and the battery cell is filled with thermally conductive interface material.

3. The high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to claim 1, characterized in that, The insulating coolant is an electronic fluorinated liquid or an aqueous solution of ethylene glycol.

4. The high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to claim 1, characterized in that, The piezoelectric micropump is an ultra-thin piezoelectric ceramic driven micropump.

5. A high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to claim 1, characterized in that, The main control unit's graded temperature control program has three preset temperature thresholds and corresponding temperature control strategies.

6. The high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to claim 1, characterized in that, The over-temperature protection unit is connected in series with the main control unit and the charge / discharge management module.

7. A high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to claim 1, characterized in that, The casing is made of glass fiber reinforced PC / ABS alloy.

8. The operating method of a high-temperature adaptive micro-pump liquid-cooled mobile power supply system as described in any one of claims 1-7, characterized in that, Includes the following steps: Step S1: Power-on self-test. After the system is powered on and started, the main control unit executes a self-test program to detect the working status of the temperature acquisition unit, piezoelectric micro-pump, charge and discharge management module, and over-temperature protection unit. After the self-test is passed, the system enters the normal working mode. Step S2: Real-time temperature acquisition. The temperature acquisition unit acquires the surface temperature of the lithium battery cell and the ambient temperature inside the casing in real time at a preset sampling frequency, and transmits the acquired temperature signal to the main control unit in real time. Step S3: Graded adaptive temperature control. The main control unit compares the real-time collected temperature data with the preset multi-level temperature thresholds, matches the corresponding temperature control strategy according to the temperature level, drives the piezoelectric micropump to adjust the coolant circulation flow rate, and realizes adaptive regulation of the cell temperature. Step S4: Multi-level safety protection. The main control unit monitors the system's operating status in real time. When the temperature reaches the current limiting protection threshold, it executes charging and discharging power limiting. When the temperature reaches the extreme over-temperature threshold, it triggers hardware-level over-temperature protection, cuts off the charging and discharging main circuit, and sends an alarm signal. After the temperature drops back to the safe range, the system automatically resumes normal operation.

9. The operating method of a high-temperature adaptive micro-pump liquid-cooled mobile power supply system according to claim 8, characterized in that, In step S3, the graded adaptive temperature control includes the following steps: Step S31: Under normal temperature and low load conditions, when the detected temperature is <45℃, the main control unit controls the piezoelectric micropump to be in a dormant state, and the system relies on the shell and heat dissipation fin assembly to achieve natural heat dissipation. Step S32, Temperature rise condition: When 45℃≤detection temperature<55℃, the main control unit outputs a PWM drive signal to control the piezoelectric micropump to operate at low flow rate, with the circulation flow rate stabilized at 30mL / min or above, and active heat dissipation is achieved through coolant circulation. Step S33, High temperature rise condition: When 55℃≤detection temperature<65℃, the main control unit increases the drive voltage to control the piezoelectric micropump to operate at high flow rate, and the circulation flow rate is stabilized at 50mL / min or above, thereby enhancing heat exchange efficiency and rapidly reducing the cell temperature. Step S34, Extreme Temperature Rise Condition: When the detected temperature is ≥65℃, the main control unit sends a current limiting command to the charge and discharge management module to reduce the charge and discharge current to 50% of the rated value. At the same time, it controls the piezoelectric micro pump to run continuously at high flow rate for strong cooling to suppress the cell temperature from rising further.

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