WO2023015410A1 - Device and method for determining thermal conductivity of insulative cushion under simulated thermal runaway - Google Patents

Device and method for determining thermal conductivity of insulative cushion under simulated thermal runaway Download PDF

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Publication number
WO2023015410A1
WO2023015410A1 PCT/CN2021/111512 CN2021111512W WO2023015410A1 WO 2023015410 A1 WO2023015410 A1 WO 2023015410A1 CN 2021111512 W CN2021111512 W CN 2021111512W WO 2023015410 A1 WO2023015410 A1 WO 2023015410A1
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WO
WIPO (PCT)
Prior art keywords
insulative
insulative cushion
cushion
pressure
heater
Prior art date
Application number
PCT/CN2021/111512
Other languages
French (fr)
Inventor
Qi SHAO
Sidi WANG
Jianping GONG
Original Assignee
Dupont (China) Research & Development And Management Co., Ltd.
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Publication date
Application filed by Dupont (China) Research & Development And Management Co., Ltd. filed Critical Dupont (China) Research & Development And Management Co., Ltd.
Priority to PCT/CN2021/111512 priority Critical patent/WO2023015410A1/en
Publication of WO2023015410A1 publication Critical patent/WO2023015410A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/18—Investigating or analyzing materials by the use of thermal means by investigating thermal conductivity
    • 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

Definitions

  • This invention relates to a device and method for determining thermal conductivity of an insulative cushion under simulated thermal runaway.
  • Multi-cell battery structures have battery cells positioned either in parallel or in series and are commonly known as battery blocks and battery packs.
  • the heat energy from unusual thermal issues, such as faults or failures, in one cell can propagate to adjacent cells. If the thermal issues are severe enough, they can propagate from cell to cell and cause a thermal runaway condition that can cascade to all the cells in the battery block or pack, resulting in a fire or even worse.
  • the batteries inevitably undergo dramatic expansion and contraction during the charge/discharge cycles, which deteriorate the electrochemical properties, liability and safety of the batteries.
  • This invention relates to a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway, comprising in order:
  • the metal block has the same surface area with the surface area of the insulative cushion.
  • This invention also relates to a method for determining thermal conductivity of an insulative cushion under simulated thermal runaway by using the device according to the present invention, comprising the following steps:
  • thermometers measuring the temperature of a front face of the insulative cushion, the temperature of a backside of the insulative cushion, and the temperature of a backside of the metal block by thermometers, wherein the front face means the surface close to the heater, and the backside means the surface away from the heater,
  • the inventors for the first time accurately simulated the real or close-to-real working scenarios of batteries which suffer from both heat release and volumetric expansion/contraction, especially under thermal runaway, and accurately measure the thermal insulation property of the insulative cushion under the simulated thermal runaway.
  • Fig. 1 schematically illustrates a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
  • Fig. 2 schematically illustrates a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
  • Fig. 3 depicts a temperature-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
  • Fig. 4 depicts a thermal conductivity-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
  • Fig. 5 depicts a temperature-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
  • Fig. 6 depicts a thermal conductivity-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
  • This invention relates to a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway, comprising in order:
  • the metal block has the same surface area with the surface area of the insulative cushion.
  • This invention also relates to a method for determining thermal conductivity of an insulative cushion under simulated thermal runaway by using the device according to the present invention, comprising the following steps:
  • thermometers measuring the temperature of a front face of the insulative cushion, the temperature of a backside of the insulative cushion, and the temperature of a backside of the metal block by thermometers, wherein the front face means the surface close to the heater, and the backside means the surface away from the heater,
  • insulation cushion it is meant a piece of material that provides either thermal insulation or volumetric buffer, or both thermal insulation and volumetric buffer.
  • the insulative cushion is a piece of material that is intended to be inserted between individual battery cells in a multi-cell battery structure.
  • the insulative cushion is used as a sample to be tested.
  • it might thermally isolate each battery cell and also mitigate the propagation of heat energy, should the battery cell develop a thermal “hot spot” or have an unusual thermal issue such as a thermal runaway, which could result in an explosion.
  • it might provide an elastic buffer zone to absorb the expansion and contraction of the cells during the charge/discharge cycles of cells so as to improve their stability and liability.
  • thermal conductivity it is not limited to an absolute value of thermal conductivity, but may be a relative or apparent value of thermal conductivity.
  • the thermal conductivity as determined herein is used to evaluate the change of the thermal conductivity of an insulative cushion under different conditions, when heat and/or pressure is applied and when heat and/or pressure is not applied.
  • the thermal conductivity as determined herein is also used to evaluate the insulative and cushioning properties of different insulative cushions when they are under the same heating and/or pressing condition.
  • backside it is meant the surface away from the heater.
  • backside of the insulative cushion it is meant the surface of the insulative cushion that is away from the heater.
  • backside of the metal block it is meant the surface of the metal block that is away from the heater.
  • front face it is meant the surface close to the heater.
  • front face of the insulative cushion it is meant the surface of the insulative cushion that is in contact with the heater.
  • front face of the metal block it is meant the surface of the metal block that is in contact with the insulative cushion.
  • the temperatures of the surfaces in contact with each other are regarded as being equal.
  • the temperature of the front face of the insulative cushion is regarded equal to the temperature of the heater.
  • the temperature of the front face of the metal block is regarded equal to the temperature of the backside of the insulative cushion.
  • the temperature of the front face of the first insulation block is regarded equal to the temperature of the backside of the metal block.
  • an insulative cushion inserted between battery cells suffers from both heat release and volumetric expansion/contraction, especially under thermal runaway.
  • an actual working scenario of an insulative cushion inserted between battery cells is simulated by carrying out the step of heating simultaneously with, before, or after the step of applying a pressure. Considering that it takes some time for the insulative cushion to reach a desired temperature upon heating, while a pressure is more instantaneously achieved, the heater may be turned on a little earlier than the starting time of the motor. However, for most of the time during the thermal runaway simulation, heat and pressure are simultaneously applied onto the insulative cushion, just like a real thermal runaway.
  • Fig. 1 schematically illustrates a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
  • the device 100 comprises in order: a motor 60 for applying a pressure onto an insulative cushion 20, a pressure sensor 50 for measuring the pressure applied onto the insulative cushion 20, a first insulation block 40, a metal block 30, an insulative cushion 20, a heater 10 for heating the insulative cushion 20, and a second insulation block 70, wherein the metal block 30 has the same surface area with the surface area of the insulative cushion 20.
  • the insulative cushion 20 is the sample to be tested. Specifically, the thermal conductivity of the sample 20 under simulated thermal runaway is to be determined. According to the present invention, since the simulated thermal runaway involves the application of both heat and pressure, the thermal conductivity thus measured is much more accurate than prior art techniques which merely consider the heat effect but ignores the volume change of the insulative cushion.
  • the insulative cushion 20 may be made from, for example, aramid material, mica, inorganic short fibers, foams, aerogels, or any combination thereof.
  • the insulative cushion 20 may be in the shape of circle, rectangular, square, oval, and any other shape as desired.
  • the insulative cushion 20 may have a thickness of about 1 mm to about 12mm.
  • the insulative cushion 20 may have a thickness of about 1 mm, 2 mm, 3 mm, 4 mm,5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, or 12 mm.
  • the insulative cushion 20 is under room temperature of about 20 to about 25 °C, corresponding to the condition of the battery pack where the cells have not started to work.
  • the heater 10 applies heat onto the insulative cushion 20, it simulates the heat energy released to the insulative cushion 20 upon cell charge/discharge during real working scenarios, especially during thermal runaway.
  • the cell reaches a peak temperature in the first few minutes, particularly in the first 1 minute.
  • the temperature decreases to a milder condition over very long period, for example, several hours, or even several days, until all exothermic reactions finish.
  • the temperature decreases significantly for at least 20 to 30 minutes with severe reactions taking place.
  • the peak temperature may be about 600 °C.
  • the peak temperature may be higher, for example, as high as about 1000 °C or even higher.
  • a heater with a rapid heating rate is preferable.
  • the heater 20 There is no specific limitation on the heater 20, and any common heater is usable so long as it does not adversely influence the effect of the present invention.
  • thermometers (indicated by the signal*in Figs 1 to 3) , preferably thermocouples, are arranged on a front face of the insulative cushion 20, a backside of the insulative cushion 20, and a backside of the metal block 30.
  • the thermometers measure the temperatures of both surfaces of the insulative cushion 20 and the top surface of the metal block 30 (i.e., the surface in contact with the second insulation block 40) .
  • the numbers of the thermometers on each surface to be tested may be the same or different, and may vary from 1 to several.
  • the number of the thermometers on each surface may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, for example, 5 thermometers on each surface.
  • thermometer may be arranged anywhere, preferably at the center point of the surface. If more than 1 thermometers are used on either surface to be tested, the thermometers may be distributed evenly or randomly, preferably evenly, at the center point and/or around the circumference of each surface, so as to collect the temperatures of the surfaces to be tested as accurate as needed.
  • the front face of the insulative cushion 20 (i.e., the surface in contact with the heater 10) is preferably heated by the heater 10 from room temperature to a peak temperature of about 600 to about 1000 °C, e.g., 600°C, 700°C, 800°C, 900 °C, or 1000 °C, during the first 1-3 minutes or the first 20 to 30 seconds.
  • the temperature of the front face of the insulative cushion 20 i.e., the temperature of the heater 10) is kept constantly at the peak temperature for a period, for example, for about 20 to 30 minutes, so as to simulate an extreme heat condition of thermal runaway.
  • the heater 10 is turned off so as to let the temperature of the front face of the insulative cushion 20 decrease to a milder temperature within a period, for example, within about 20 to 30 minutes.
  • the metal block 30 has the same surface area with the surface area of the insulative cushion 20.
  • the metal block 30 has the same surface shape with the surface shape of the insulative cushion 20, so that they perfectly match with each other.
  • the front face of the metal block 30 and the backside of the insulative cushion 20, which are in contact with each other, have the same shape and same area.
  • the metal block 30 is preferably made from stainless steel or aluminum. Stainless steel is more preferable because of its mature processing techniques and availability of thermal conductivity data.
  • q x represents the heat energy transferred across the thickness direction x of a medium
  • k represents the thermal conductivity of the medium
  • A represents the heat transfer area
  • dT/dx represents the temperature gradient across the thickness x of the medium.
  • the parameter k of the metal block 30 is inherent and known.
  • the surface area A of the metal block 30 is equal to the surface area A’ of the insulative cushion 20.
  • the temperatures (T, T’) and thicknesses (x, x’) of both the metal block 30 and the insulative cushion 20 are measurable.
  • the q x of the metal block 30 is equal to the (q x ) ’ of the insulative cushion 20, as mentioned above.
  • the conductivity k’ of the insulative cushion 20 can be calculated from the following Fourier’s Law equation.
  • a control panel, or a calculation module, may be electrically, communicationally, and/or mechanically connected with the device 100, so as to receive temperature data from the thermometers, receive pressure data from the press sensor 50, and any other data (e.g., depth of the insulative cushion 20) when needed, and output the conductivity of the insulative cushion 20 under different heat and pressure conditions.
  • the first insulation block 40 prevents heat from being dissipated from the backside of the metal block 30 so as to ensure the accuracy of the heat conductivity measurement, and also protects the pressure sensor from being overheated.
  • the first insulation block 40 has a surface larger than or same with the backside of the metal block 30 so as to sufficiently cover the backside of the metal block 30, and block heat dissipation from the backside of the metal block 30.
  • the motor 60 does not apply a pressure onto the insulative cushion 20, the insulative cushion 20 is under atmospheric pressure or its natural state (compared with the pressed state) .
  • the motor 60 applies a pressure onto the insulative cushion 20, it simulates the pressure suffered from by the insulative cushion 20 upon cell expansion/contraction during real working scenarios, especially during thermal runaway.
  • the cells expand significantly, and for prismatic cells, the cells also release hot gas from a valve. Then, the cells shrink back to a state similar with a condition where they have not started to work.
  • the pressure applied by the motor 60 is preferably increased within the first 1 minute or the first 20 to 30 seconds to no more than 5 MPa, e.g., about 0.1 MPa, about 0.2 MPa, about 0.3 MPa, about 0.4 MPa, about 0.5 MPa, about 0.9 MPa, about 1 MPa, about 1.5 MPa, about 2 MPa, about 2.5 MPa, about 3 MPa, about 3.5 MPa, about 4 MPa, about 4.5 MPa, about 5 MPa.
  • 5 MPa e.g., about 0.1 MPa, about 0.2 MPa, about 0.3 MPa, about 0.4 MPa, about 0.5 MPa, about 0.9 MPa, about 1 MPa, about 1.5 MPa, about 2 MPa, about 2.5 MPa, about 3 MPa, about 3.5 MPa, about 4 MPa, about 4.5 MPa, about 5 MPa.
  • the pressure is kept constantly for about 20 to 30 minutes.
  • the pressure is decreases to a lower pressure for about 20 to 30 minutes.
  • the pressure applied by the motor 60 is presumed equal with the pressure applied onto the insulative cushion 20, as if the pressure is directly applied by the motor 60 onto the insulative cushion 20.
  • the motor may be a hydraulic system.
  • the motor is a servo motor system, so that the displacement of the insulative cushion 20 is accurately controllable.
  • the pressure sensor 50 in direct contact with the motor 60 measures the pressure applied by the motor 60 onto the insulative cushion 20.
  • the device 100 comprises a second insulation block 70 (see Fig. 1) .
  • the second insulation block 70 may also be in the form of one or more insulation rods 71, 72 (see Fig. 2) .
  • the device 100 may additionally comprise a frame (or case) 80 to encapsulate, protect, vent and/or evacuate the device 100.
  • the frame is preferably made from metal.
  • An auto shut-down with a door opening and/or temperature limit may be located on the frame. The temperature limit holds the frame locked when ambient temperature is higher than a given temperature.
  • the device 100 according to the present invention may additionally comprise an extensiometer (not shown) , preferable a contact extensiometer, to monitor the thickness change of the insulative cushion 20 under different pressures.
  • an extensiometer (not shown) , preferable a contact extensiometer, to monitor the thickness change of the insulative cushion 20 under different pressures.
  • MDME302GCGMDME302GCGM Samsung Motor: MDME302GCGMDME302GCGM, Panasonic,
  • First insulation block Ceramic block, 10cm*10cm, 200mm,
  • Metal block stainless steel, 10cm*10cm, 30mm,
  • An insulative cushion CellShield TM , 10cm*10cm, 2.43mm, available from E.I. du Pont de Nemours and Co., Wilmington, Delaware (DuPont)
  • Second insulation block Ceramic block, 30cm*30cm, 200mm
  • thermocouples were arranged on the backside of the Cell Shield TM sample, and the backside of the metal block.
  • the heater and motor were turned on.
  • the temperature of the heater was increased to a peak temperature about 600 °C in the first 1 minute.
  • the peak temperature of about 600 °C was maintained for about 30 minutes.
  • the pressure applied by the motor 60 was increased to about 0.2 MPa within the first 2 mins,. and then kept at about 0.2 MPa for about 30 minutes.
  • Fig. 3 depicts temperature-time profiles of the two sides of the insulative cushion as well as the heater, and Fig. 4 depicts an apparent thermal conductivity-time profile of the insulative cushion.
  • the heater and motor were turned on.
  • the temperature of the heater was increased to a peak temperature about 600 °C in the first 1 minute.
  • Then the heater was turned off.
  • the pressure applied by the motor 60 was increased to about 0.5 MPa within the first 1 min,. and then kept at about 0.2 MPa for about 30 minutes.
  • Fig. 5 depicts temperature-time profiles of the two sides of the insulative cushion as well as the heater
  • Fig. 6 depicts an apparent thermal conductivity-time profile of the insulative cushion.

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Abstract

Provided is a device (100) for determining thermal conductivity of an insulative cushion (20) under simulated thermal runaway, comprising in order: a motor (60) for applying a pressure onto an insulative cushion (20), a pressure sensor (50) for measuring the pressure applied onto the insulative cushion (20), a first insulation block (40), a metal block (30), the insulative cushion (20), a heater (10) for heating the insulative cushion (20), and a second insulation block (70), wherein the metal block (30) has the same surface area with the surface area of the insulative cushion (20). Also provided is a method for determining thermal conductivity of an insulative cushion (20) under simulated thermal runaway by using the device.

Description

DEVICE AND METHOD FOR DETERMINING THERMAL CONDUCTIVITY OF INSULATIVE CUSHION UNDER SIMULATED THERMAL RUNAWAY Technical Field
This invention relates to a device and method for determining thermal conductivity of an insulative cushion under simulated thermal runaway.
Background
Multi-cell battery structures have battery cells positioned either in parallel or in series and are commonly known as battery blocks and battery packs. In these multi-cell battery structures, the heat energy from unusual thermal issues, such as faults or failures, in one cell can propagate to adjacent cells. If the thermal issues are severe enough, they can propagate from cell to cell and cause a thermal runaway condition that can cascade to all the cells in the battery block or pack, resulting in a fire or even worse. In addition, especially for lithium-ion batteries, the batteries inevitably undergo dramatic expansion and contraction during the charge/discharge cycles, which deteriorate the electrochemical properties, liability and safety of the batteries.
It is known to use an insulative cushion to separate battery cells, prevent overheating and hot spots in one cell from causing the entire battery pack to evolve into a thermal runaway condition that could result in fire or explosion, and withstand the dramatic volumetric change during the charge/discharge cycles.
As for the thermal insulation property of the insulative cushion, so far commercially available devices merely evaluate its conductive coefficient by determining the heat input into and output from the insulative cushion.
However, there is a need to accurately measure the thermal insulation property of an insulative cushion under real or close-to-real working scenarios of batteries which suffer from both heat release and volumetric expansion/contraction, especially under thermal runaway.
Brief Summary of the Invention
This invention relates to a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway, comprising in order:
- a motor for applying a pressure onto an insulative cushion,
- a pressure sensor for measuring the pressure applied onto the insulative cushion,
- a first insulation block,
- a metal block,
- the insulative cushion,
- a heater for heating the insulative cushion, and
- a second insulation block,
wherein the metal block has the same surface area with the surface area of the insulative cushion.
This invention also relates to a method for determining thermal conductivity of an insulative cushion under simulated thermal runaway by using the device according to the present invention, comprising the following steps:
- heating the insulative cushion by the heater,
- applying a pressure onto the insulative cushion by the motor,
- measuring the temperature of a front face of the insulative cushion, the temperature of a backside of the insulative cushion, and the temperature of a backside of the metal block by thermometers, wherein the front face means the surface close to the heater, and the backside means the surface away from the heater,
- measuring the pressure applied onto the insulative cushion by the pressure sensor, and
- calculating the thermal conductivity of the insulative cushion under a desired heat and pressure.
By the device and/or method according to the present invention, the inventors for the first time accurately simulated the real or close-to-real working scenarios of batteries which suffer from both heat release and volumetric expansion/contraction, especially under thermal runaway, and accurately measure the thermal insulation property of the insulative cushion under the simulated thermal runaway.
Brief Description of the Drawings
Fig. 1 schematically illustrates a device for determining thermal conductivity of  an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
Fig. 2 schematically illustrates a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
Fig. 3 depicts a temperature-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
Fig. 4 depicts a thermal conductivity-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
Fig. 5 depicts a temperature-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
Fig. 6 depicts a thermal conductivity-time profile of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention.
The figures are not drawn to scale, and are provided merely for illustrative purpose, but are in no way construed as limitative purpose.
In different Figs, like numbers refer to like elements.
Detailed Description of the Invention
This invention relates to a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway, comprising in order:
- a motor for applying a pressure onto an insulative cushion,
- a pressure sensor for measuring the pressure applied onto the insulative cushion,
- a first insulation block,
- a metal block,
- the insulative cushion,
- a heater for heating the insulative cushion, and
- a second insulation block,
wherein the metal block has the same surface area with the surface area of the insulative cushion.
This invention also relates to a method for determining thermal conductivity of an insulative cushion under simulated thermal runaway by using the device according to the present invention, comprising the following steps:
- heating the insulative cushion by the heater,
- applying a pressure onto the insulative cushion by the motor,
- measuring the temperature of a front face of the insulative cushion, the temperature of a backside of the insulative cushion, and the temperature of a backside of the metal block by thermometers, wherein the front face means the surface close to the heater, and the backside means the surface away from the heater,
- measuring the pressure applied onto the insulative cushion by the pressure sensor, and
- calculating the thermal conductivity of the insulative cushion under a desired heat and pressure.
By “insulative cushion” , it is meant a piece of material that provides either thermal insulation or volumetric buffer, or both thermal insulation and volumetric buffer.
According to the present invention, the insulative cushion is a piece of material that is intended to be inserted between individual battery cells in a multi-cell battery structure. The insulative cushion is used as a sample to be tested. On the one hand, it might thermally isolate each battery cell and also mitigate the propagation of heat energy, should the battery cell develop a thermal “hot spot” or have an unusual thermal issue such as a thermal runaway, which could result in an explosion. On the other hand, it might provide an elastic buffer zone to absorb the expansion and contraction of the cells during the charge/discharge cycles of cells so as to improve their stability and liability.
By “thermal conductivity” , it is not limited to an absolute value of thermal conductivity, but may be a relative or apparent value of thermal conductivity. The thermal conductivity as determined herein is used to evaluate the change of the thermal conductivity of an insulative cushion under different conditions,  when heat and/or pressure is applied and when heat and/or pressure is not applied. The thermal conductivity as determined herein is also used to evaluate the insulative and cushioning properties of different insulative cushions when they are under the same heating and/or pressing condition.
By “backside” , it is meant the surface away from the heater. By “backside of the insulative cushion” , it is meant the surface of the insulative cushion that is away from the heater. By “backside of the metal block” , it is meant the surface of the metal block that is away from the heater.
In contrast, by “front face” , it is meant the surface close to the heater. By “front face of the insulative cushion” , it is meant the surface of the insulative cushion that is in contact with the heater. By “front face of the metal block” , it is meant the surface of the metal block that is in contact with the insulative cushion.
The temperatures of the surfaces in contact with each other are regarded as being equal. For example, the temperature of the front face of the insulative cushion is regarded equal to the temperature of the heater. The temperature of the front face of the metal block is regarded equal to the temperature of the backside of the insulative cushion. The temperature of the front face of the first insulation block is regarded equal to the temperature of the backside of the metal block.
In actual working situations, an insulative cushion inserted between battery cells suffers from both heat release and volumetric expansion/contraction, especially under thermal runaway. In the present invention, an actual working scenario of an insulative cushion inserted between battery cells is simulated by carrying out the step of heating simultaneously with, before, or after the step of applying a pressure. Considering that it takes some time for the insulative cushion to reach a desired temperature upon heating, while a pressure is more instantaneously achieved, the heater may be turned on a little earlier than the starting time of the motor. However, for most of the time during the thermal runaway simulation, heat and pressure are simultaneously applied onto the insulative cushion, just like a real thermal runaway.
Fig. 1 schematically illustrates a device for determining thermal conductivity of an insulative cushion under simulated thermal runaway according to one embodiment of the present invention. The device 100 comprises in order: a  motor 60 for applying a pressure onto an insulative cushion 20, a pressure sensor 50 for measuring the pressure applied onto the insulative cushion 20, a first insulation block 40, a metal block 30, an insulative cushion 20, a heater 10 for heating the insulative cushion 20, and a second insulation block 70, wherein the metal block 30 has the same surface area with the surface area of the insulative cushion 20.
The insulative cushion 20 is the sample to be tested. Specifically, the thermal conductivity of the sample 20 under simulated thermal runaway is to be determined. According to the present invention, since the simulated thermal runaway involves the application of both heat and pressure, the thermal conductivity thus measured is much more accurate than prior art techniques which merely consider the heat effect but ignores the volume change of the insulative cushion.
There is no specific limitation on the material, shape, and/or size of the insulative cushion 20, and any insulative cushion commonly used in cell packs is usable. For example, the insulative cushion 20 may be made from, for example, aramid material, mica, inorganic short fibers, foams, aerogels, or any combination thereof. The insulative cushion 20 may be in the shape of circle, rectangular, square, oval, and any other shape as desired. The insulative cushion 20 may have a thickness of about 1 mm to about 12mm. For example, the insulative cushion 20 may have a thickness of about 1 mm, 2 mm, 3 mm, 4 mm,5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, or 12 mm.
If the heater 10 does not apply heat onto the insulative cushion 20, the insulative cushion 20 is under room temperature of about 20 to about 25 ℃, corresponding to the condition of the battery pack where the cells have not started to work.
If the heater 10 applies heat onto the insulative cushion 20, it simulates the heat energy released to the insulative cushion 20 upon cell charge/discharge during real working scenarios, especially during thermal runaway. During the initial stage of real thermal runaway, tremendous amount of heat is released within a short period, and the cell reaches a peak temperature in the first few minutes, particularly in the first 1 minute. Then, the temperature decreases to a milder condition over very long period, for example, several hours, or even several days, until all exothermic reactions finish. For example, the  temperature decreases significantly for at least 20 to 30 minutes with severe reactions taking place. For NCM 523 cell, the peak temperature may be about 600 ℃. For cells with higher density, such as NCM 811, the peak temperature may be higher, for example, as high as about 1000 ℃ or even higher.
In order to accurately simulate the temperature increase/decrease process in thermal runaway, a heater with a rapid heating rate is preferable. There is no specific limitation on the heater 20, and any common heater is usable so long as it does not adversely influence the effect of the present invention.
In some examples, thermometers (indicated by the signal*in Figs 1 to 3) , preferably thermocouples, are arranged on a front face of the insulative cushion 20, a backside of the insulative cushion 20, and a backside of the metal block 30. The thermometers measure the temperatures of both surfaces of the insulative cushion 20 and the top surface of the metal block 30 (i.e., the surface in contact with the second insulation block 40) . The numbers of the thermometers on each surface to be tested may be the same or different, and may vary from 1 to several. For example, the number of the thermometers on each surface may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, for example, 5 thermometers on each surface. If 1 thermometer is used on either surface to be tested, it may be arranged anywhere, preferably at the center point of the surface. If more than 1 thermometers are used on either surface to be tested, the thermometers may be distributed evenly or randomly, preferably evenly, at the center point and/or around the circumference of each surface, so as to collect the temperatures of the surfaces to be tested as accurate as needed.
In some examples, the front face of the insulative cushion 20 (i.e., the surface in contact with the heater 10) is preferably heated by the heater 10 from room temperature to a peak temperature of about 600 to about 1000 ℃, e.g., 600℃, 700℃, 800℃, 900 ℃, or 1000 ℃, during the first 1-3 minutes or the first 20 to 30 seconds.
Then the temperature of the front face of the insulative cushion 20 (i.e., the temperature of the heater 10) is kept constantly at the peak temperature for a period, for example, for about 20 to 30 minutes, so as to simulate an extreme heat condition of thermal runaway.
Alternatively, the heater 10 is turned off so as to let the temperature of the front  face of the insulative cushion 20 decrease to a milder temperature within a period, for example, within about 20 to 30 minutes.
The metal block 30 has the same surface area with the surface area of the insulative cushion 20. Preferably, the metal block 30 has the same surface shape with the surface shape of the insulative cushion 20, so that they perfectly match with each other. Particularly, the front face of the metal block 30 and the backside of the insulative cushion 20, which are in contact with each other, have the same shape and same area. On this basis, we theoretically or ideally presume that the amount of heat energy passing through the metal block 30 is equal to the amount of heat energy passing through the insulative cushion 20. The metal block 30 is preferably made from stainless steel or aluminum. Stainless steel is more preferable because of its mature processing techniques and availability of thermal conductivity data.
According to the Fourier’s Law equation as below, q x represents the heat energy transferred across the thickness direction x of a medium, k represents the thermal conductivity of the medium, A represents the heat transfer area, and dT/dx represents the temperature gradient across the thickness x of the medium.
Figure PCTCN2021111512-appb-000001
The parameter k of the metal block 30 is inherent and known. The surface area A of the metal block 30 is equal to the surface area A’ of the insulative cushion 20. The temperatures (T, T’) and thicknesses (x, x’) of both the metal block 30 and the insulative cushion 20 are measurable. Not wishing to be constrained by theory, we assume that the q x of the metal block 30 is equal to the (q x) ’ of the insulative cushion 20, as mentioned above. Thus, the conductivity k’ of the insulative cushion 20 can be calculated from the following Fourier’s Law equation.
Figure PCTCN2021111512-appb-000002
A control panel, or a calculation module, (not shown in the Figs) may be electrically, communicationally, and/or mechanically connected with the device 100, so as to receive temperature data from the thermometers, receive pressure data from the press sensor 50, and any other data (e.g., depth of the insulative cushion 20) when needed, and output the conductivity of the  insulative cushion 20 under different heat and pressure conditions.
The first insulation block 40 prevents heat from being dissipated from the backside of the metal block 30 so as to ensure the accuracy of the heat conductivity measurement, and also protects the pressure sensor from being overheated.
There is no specific limitation on the material, size, and/or weight of the first insulation block 40, so long as it does not adversely influence the effect of the present invention. The first insulation block 40 has a surface larger than or same with the backside of the metal block 30 so as to sufficiently cover the backside of the metal block 30, and block heat dissipation from the backside of the metal block 30.
If the motor 60 does not apply a pressure onto the insulative cushion 20, the insulative cushion 20 is under atmospheric pressure or its natural state (compared with the pressed state) .
If the motor 60 applies a pressure onto the insulative cushion 20, it simulates the pressure suffered from by the insulative cushion 20 upon cell expansion/contraction during real working scenarios, especially during thermal runaway. During the initial stage of real thermal runaway, the cells expand significantly, and for prismatic cells, the cells also release hot gas from a valve. Then, the cells shrink back to a state similar with a condition where they have not started to work.
In some examples, the pressure applied by the motor 60 is preferably increased within the first 1 minute or the first 20 to 30 seconds to no more than 5 MPa, e.g., about 0.1 MPa, about 0.2 MPa, about 0.3 MPa, about 0.4 MPa, about 0.5 MPa, about 0.9 MPa, about 1 MPa, about 1.5 MPa, about 2 MPa, about 2.5 MPa, about 3 MPa, about 3.5 MPa, about 4 MPa, about 4.5 MPa, about 5 MPa.
Subsequently, the pressure is kept constantly for about 20 to 30 minutes. Alternatively, the pressure is decreases to a lower pressure for about 20 to 30 minutes.
The pressure applied by the motor 60 is presumed equal with the pressure  applied onto the insulative cushion 20, as if the pressure is directly applied by the motor 60 onto the insulative cushion 20.
There is no specific limitation on the motor, and any motor commonly used to apply a pressure is usable. For example, the motor may be a hydraulic system. Preferably, the motor is a servo motor system, so that the displacement of the insulative cushion 20 is accurately controllable.
The pressure sensor 50 in direct contact with the motor 60 measures the pressure applied by the motor 60 onto the insulative cushion 20.
The device 100 according to the present invention comprises a second insulation block 70 (see Fig. 1) . There is no specific limitation on the material, size, and/or weight of the second insulation block 70, so long as it sufficiently blocks heat dissipation from the bottom of the heater 10. The second insulation block 70 may also be in the form of one or more insulation rods 71, 72 (see Fig. 2) .
The device 100 according to the present invention may additionally comprise a frame (or case) 80 to encapsulate, protect, vent and/or evacuate the device 100. The frame is preferably made from metal. An auto shut-down with a door opening and/or temperature limit may be located on the frame. The temperature limit holds the frame locked when ambient temperature is higher than a given temperature.
The device 100 according to the present invention may additionally comprise an extensiometer (not shown) , preferable a contact extensiometer, to monitor the thickness change of the insulative cushion 20 under different pressures.
Examples
Motor: MDME302GCGMDME302GCGM, Panasonic,
Pressure sensor: NS-TH3B-5T, TM
First insulation block: Ceramic block, 10cm*10cm, 200mm,
Metal block: stainless steel, 10cm*10cm, 30mm,
An insulative cushion: 
Figure PCTCN2021111512-appb-000003
CellShield TM, 10cm*10cm, 2.43mm, available from E.I. du Pont de Nemours and Co., Wilmington, Delaware (DuPont) Second insulation block: Ceramic block, 30cm*30cm, 200mm
As shown in Fig. 1, a heater was placed onto the surface of the second insulation block. A motor and a pressure sensor were assembled together. The 
Figure PCTCN2021111512-appb-000004
CellShield TM sample, the metal block and the first insulation block was placed onto the heater. 5 thermocouples were arranged on the backside of the
Figure PCTCN2021111512-appb-000005
Cell Shield TMsample, and the backside of the metal block.
Example 1
The heater and motor were turned on. The temperature of the heater was increased to a peak temperature about 600 ℃ in the first 1 minute. Then the peak temperature of about 600 ℃ was maintained for about 30 minutes. The pressure applied by the motor 60 was increased to about 0.2 MPa within the first 2 mins,. and then kept at about 0.2 MPa for about 30 minutes.
By collecting the temperature data displayed on a screen panel, Fig. 3 depicts temperature-time profiles of the two sides of the insulative cushion as well as the heater, and Fig. 4 depicts an apparent thermal conductivity-time profile of the insulative cushion.
It can be seen that under simulated thermal runaway conditions which involved both high temperature and high pressure, the thermal conductivity of the insulative cushion was accurately measured. The thermal conductivity in Fig. 4 slowly decreased, which is presumably attributed to the inherent properties of the
Figure PCTCN2021111512-appb-000006
CellShield TM sample. In most cases where an insulative cushion other than the specific
Figure PCTCN2021111512-appb-000007
CellShield TM sample is used, the thermal conductivity tends to be relatively constant.
Example 2
The heater and motor were turned on. The temperature of the heater was increased to a peak temperature about 600 ℃ in the first 1 minute. Then the heater was turned off. The pressure applied by the motor 60 was increased to about 0.5 MPa within the first 1 min,. and then kept at about 0.2 MPa for about 30 minutes.
By collecting the temperature data displayed on a screen panel, Fig. 5 depicts temperature-time profiles of the two sides of the insulative cushion as well as  the heater, and Fig. 6 depicts an apparent thermal conductivity-time profile of the insulative cushion.
It can be seen that under simulated thermal runaway conditions which involved both high temperature and high pressure, the thermal conductivity of the insulative cushion was accurately measured. The thermal conductivity in Fig. 6 increased within the first 2 minutes, then fluctuated down and up from the 2 nd minute to the 5 th minute, and kept relatively constant after the first 5 minutes, because from then on, the pressure reached a constant level. The thermal conductivity in Fig. 6 fluctuated from the 2 nd minute to the 5 th minute, which is presumably attributed to the inherent properties of the
Figure PCTCN2021111512-appb-000008
CellShield TM sample. In other cases where an insulative cushion other than the specific 
Figure PCTCN2021111512-appb-000009
CellShield TM sample is used, if thermal insulation properties do not change much due to compression, the thermal conductivity tends to be relatively constant after the first 2 minutes’ increase, without the significant down-and-up fluctuation.

Claims (10)

  1. A device for determining thermal conductivity of an insulative cushion under simulated thermal runaway, comprising in order:
    - a motor for applying a pressure onto an insulative cushion,
    - a pressure sensor for measuring the pressure applied onto the insulative cushion,
    - a first insulation block,
    - a metal block,
    - the insulative cushion,
    - a heater for heating the insulative cushion, and
    - a second insulation block,
    wherein the metal block has the same surface area with the surface area of the insulative cushion.
  2. The device according to claim I, wherein thermometers, preferably thermocouples, are arranged on a backside of the insulative cushion and a backside of the metal block.
  3. The device according to claim 1 or 2, wherein the motor is a servo motor system.
  4. The device according to any one of claims 1 to 3, further comprising a frame or case to encapsulate the device.
  5. The device according to any one of claims 1 to 4, further comprising an extensiometer, preferable a contact extensiomer, to monitor the thickness change of the insulative cushion under different pressures.
  6. The device according to any one of claims 1 to 5, further comprising a control panel, which is electrically, communicationally, and/or mechanically connected with the device.
  7. A method for determining thermal conductivity of an insulative cushion under simulated thermal runaway by using the device according to the present invention, comprising the following steps:
    - heating the insulative cushion by the heater,
    - applying a pressure onto the insulative cushion by the motor,
    - measuring the temperature of a front face of the insulative cushion, the temperature of a backside of the insulative cushion, and the temperature of a backside of the metal block by thermometers, wherein the front face means the surface close to the heater, and the backside means the surface away from the heater,
    - measuring the pressure applied onto the insulative cushion by the pressure sensor, and
    - calculating the thermal conductivity of the insulative cushion under a desired heat and pressure.
    .
  8. The method according to claim 7, wherein the insulative cushion is heated from room temperature to a peak temperature of about 600 to about 1000 ℃ during the first few minutes, particularly in the first 1-3 minute.
  9. The method according to claim 7 or 8, wherein the pressure is increased to no more than 5 MPa during the first 20 to 30 seconds.
  10. The method according to any one of claims 7 to 9, wherein the step of heating is carried out simultaneously with, before, or after the step of applying a pressure.
PCT/CN2021/111512 2021-08-09 2021-08-09 Device and method for determining thermal conductivity of insulative cushion under simulated thermal runaway WO2023015410A1 (en)

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US20120018415A1 (en) * 2010-07-20 2012-01-26 University Of Houston Self-heating concrete using carbon nanofiber paper
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* Cited by examiner, † Cited by third party
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CN101303320A (en) * 2008-06-06 2008-11-12 西安交通大学 Quasi-stable state method solid body thermal conductivity measurement instrument
US20120018415A1 (en) * 2010-07-20 2012-01-26 University Of Houston Self-heating concrete using carbon nanofiber paper
CN101949873A (en) * 2010-10-11 2011-01-19 华东师范大学 Device for measuring solid material heat conductivity
CN103983662A (en) * 2014-05-28 2014-08-13 南京玻璃纤维研究设计院有限公司 Measurement method of heat conductivity coefficient of thermal insulation coating
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