The present disclosure is directed at a method, system, and apparatus for inhibiting thermal runaway of a battery cell.
Thermal runaway of a battery cell refers to a positive feedback process by which the temperature of the battery cell increases as a result of an exothermic reaction. The exothermic reaction may, for example, result from discharging excessive current from the battery cell or from operating the battery cell in an excessively hot environment. Eventually, uncontrolled thermal runaway causes one or both of the battery cell's temperature and pressure to increase to the extent that the battery cell may combust, explode, or both.
The pressure inside the battery cell also increases as the battery cell experiences thermal runaway. At its peak, slightly before the thermal runaway end point 18, this pressure is approximately 64 bar. Accordingly, at the thermal runaway end point 18, the battery cell is prone to one or both of explosion and combustion. In an effort to prevent these undesirable outcomes, research and development continue into methods, systems, and apparatuses to inhibit thermal runaway.
According to a first aspect, there is provided an apparatus for inhibiting thermal runaway of a battery cell, the apparatus comprising a temperature sensor positioned to measure a temperature of the cell; and a discharge circuit, comprising a switch and a resistive load electrically coupled in series across terminals of the cell, wherein the switch is closed when the temperature sensor detects that the temperature of the cell has exceeded a maximum normal operating temperature.
The switch may be open when the temperature sensor detects that the temperature of the cell is below the maximum normal operating temperature.
The apparatus may further comprise a thermally controlled switching device that has a positive temperature coefficient and that is electrically connected in series between a voltage source of the battery cell and one of the terminals of the battery cell.
The apparatus may comprise battery cells electrically connected in parallel, wherein each of the battery cells comprises a thermally controlled switching device that has a positive temperature coefficient and that is electrically connected in series between a voltage source of the battery cell and one of the terminals of the battery cell.
The thermally controlled switching device may have a switch temperature that exceeds the maximum normal operating temperature of the cell in which the thermally controlled switching device is contained.
The thermally controlled switching device may comprise a polymeric positive temperature coefficient device, a semiconductor sensor, a resistance thermometer, a resistance temperature detector, a thermocouple, a thermopile, an infrared sensor, a thermistor, or a non-resettable fuse.
The apparatus may further comprise a comparator having an input driven by the temperature sensor and an output that drives the switch.
The apparatus may further comprise a processor having an input driven by the temperature sensor and an output that drives the switch; and a non-transitory computer readable medium, communicatively coupled to the processor, and having encoded thereon program code that causes the processor to perform a method comprising (i) determining the temperature of the cell from the temperature sensor; and (ii) when the temperature of the cell exceeds the maximum normal operating temperature, decreasing the state of charge (“SOC”) of the cell to a safe SOC.
The battery cell may comprise part of one of multiple series elements electrically connected in series, wherein each of the series elements comprises additional battery cells electrically connected in parallel.
The apparatus may further comprise additional temperature sensors positioned to measure temperatures of at least some of the additional battery cells, wherein the additional temperature sensors are communicatively coupled to the processor.
When the temperature of the cell exceeds a self-heating temperature of the cell, the processor may decrease the SOC to a minimum SOC of the cell.
When the temperature of the cell exceeds a warning temperature of the cell that is between the maximum normal operating temperature and the self-heating temperature, the processor may decrease the SOC to be above the minimum SOC and below a maximum SOC of the cell.
According to another aspect, there is provided a battery pack comprising battery cells electrically connected in parallel with each other, wherein each of the battery cells comprises a thermally controlled switching device that has a positive temperature coefficient and that is electrically connected in series between a voltage source of the battery cell and a terminal of the battery cell.
The thermally controlled switching device may comprise a polymeric positive temperature coefficient device, a semiconductor sensor, a resistance thermometer, a resistance temperature detector, a thermocouple, a thermopile, an infrared sensor, a thermistor, or a non-resettable fuse.
According to another aspect, there is provided a method for inhibiting thermal runaway of a battery cell, the method comprising determining the temperature of the cell; and when the temperature of the cell exceeds a maximum normal operating temperature of the cell, decreasing the SOC of the cell to a safe SOC.
The battery cell may comprise part of one of multiple series elements electrically connected in series, wherein each of the series elements comprises additional battery cells electrically connected in parallel.
When the temperature of the cell exceeds a self-heating temperature of the cell, the method may further comprise decreasing the SOC to a minimum SOC of the cell.
The method may further comprise when the temperature of the cell exceeds a warning temperature of the cell that is between the maximum normal operating temperature and the self-heating temperature, decreasing the SOC to be above the minimum SOC and below a maximum SOC of the cell.
According to another aspect, there is provided a non-transitory computer readable medium having encoded thereon statements and instructions to cause a processor to perform any aspects of the foregoing method.
This summary does not necessarily describe the entire scope of all aspects. Other aspects, features and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.
In the accompanying drawings, which illustrate one or more example embodiments:
Directional terms such as “top”, “bottom”, “upwards”, “downwards”, “vertically”, and “laterally” are used in the following description for the purpose of providing relative reference only, and are not intended to suggest any limitations on how any article is to be positioned during use, or to be mounted in an assembly or relative to an environment. Additionally, the term “couple” and variants of it such as “coupled”, “couples”, and “coupling” as used in this description is intended to include indirect and direct connections unless otherwise indicated. For example, if a first device is coupled to a second device, that coupling may be through a direct connection or through an indirect connection via other devices and connections. Similarly, if the first device is communicatively coupled to the second device, communication may be through a direct connection or through an indirect connection via other devices and connections.
As shown in
The embodiments described herein are directed at inhibiting thermal runaway by inhibiting self-heating. The temperature of the battery cell is measured using a temperature sensor to determine whether the battery cell has begun self-heating and, if so, to estimate its severity. If the battery cell is determined to be self-heating, the battery cell is discharged to reduce its SOC and to reduce the rate of self-heating or to stop the self-heating altogether.
The example embodiments below focus on various lithium ion battery chemistries. Example lithium ion battery chemistries include lithium cobalt oxide (LiCoO2), lithium iron phosphate (LFP), lithium manganese dioxide (LMO), lithium nickel manganese cobalt (NMC), lithium nickel cobalt oxide (NCO), and lithium titanate (LTO). The example embodiments below also may be applied to battery cells packaged in different styles. Example packaging styles include cylindrical jelly roll (liquid and polymer gel electrolytes), prismatic (liquid electrolyte), and pouch (liquid and polymer gel electrolytes for a single layer electrode, and liquid electrolyte for a multi-layered electrode). Example capacities for a single battery cell range, for example, from 50 mAh to 250 Ah.
While the example embodiments below focus on lithium ion batteries, alternative embodiments (not depicted) may be used in conjunction with battery cells of different chemistries. Similarly, alternative embodiments (not depicted) may be directed at battery cells having capacities and packaging styles different from those listed above.
Referring now to
The apparatus 100 further comprises a discharge circuit comprising a resistive load 110 and a transistor 112 connected in series across the terminals 108. The discharge circuit may comprise part of cell balancing circuitry electrically coupled to the battery cell; alternatively, the discharge circuit may be independent from the cell balancing circuitry, which may permit the discharge circuit to discharge the battery cell at a higher rate than would be possible if the cell balancing circuitry were used for discharge. While the transistor 112 is shown as being a MOSFET, in alternative embodiments the transistor 112 may be another suitable type of transistor, such as a BJT or IGBT, or more generally any suitable type of switching device, such as a mechanical relay or switch (e.g. a contactor).
Also comprising part of the apparatus 100 are a temperature sensor in the form of a thermocouple 116 having positive and negative terminals, and an operational amplifier in an open-loop configuration whose non-inverting and inverting inputs are connected to the thermocouple's 116 positive and negative terminals, respectively (the operational amplifier is hereinafter the “comparator 114”). The comparator 114 is powered by positive and negative voltage supplies, which are respectively labeled in
While the temperature sensor in
In
Referring now to
A PTC is a thermally activated device that operates in a low impedance states (e.g. the PTC has an impedance of <0.03Ω) when used in normal temperatures (e.g. ˜23° C.) and a high impedance state (e.g. the PTC has an impedance of >100Ω) when used in high temperatures (e.g. ˜100° C.). The temperature at which the PTCs 118a-c transition between their low and high impedance states is known as their “switch temperature”. The PTCs 118a-c may be, for example, the MF-SVS line of PTCs from Bourns®, Inc. Different types of PTCs have different switch temperatures; example switch temperatures include 85° C. and 150° C.
The apparatus 100 of
In the event self-heating is not sufficiently inhibited by the discharge circuitry alone and the temperature of any one or more of the battery cells exceeds the switch temperature of the PTCs 118a-c, the PTCs 118a-c for those battery cells will transition to their high impedance state. This electrically isolates those battery cells from the remainder of the battery cells connected to it in parallel, which further inhibits self-heating. Instead of the PTCs 118a-c, any suitable thermally controlled switching device having a positive temperature coefficient may be used; these thermally controlled switching devices comprise temperature sensors such as semiconductor sensors (whether voltage output, current output, resistance output, digital output, or simple diode types of semiconductor sensors), resistance thermometers/resistance temperature detectors, thermocouples, thermopiles, infrared sensors, thermistors, and non-resettable fuses. Some of these temperature sensors, such as thermistors and non-resettable fuses, inherently increase in resistance as temperature increases, permitting them to be used in place of the PTCs 118a-c without any ancillary switching circuitry. Others of these thermal measurement devices, such as voltage output semiconductor sensors and thermocouples, are used to drive switching circuitry to act as an open circuit when the temperature exceeds a safe operating threshold.
Referring now to
Each of the series elements 406a-c is identical to the embodiment of the apparatus 100 of
In the embodiment of
The system 400 further comprises a processor 402 communicatively coupled to the output of each of the thermocouples 116a-i and to the gates of each of the transistors 112 of the series elements 406a-c. The processor 402 includes an analog-to-digital converter to digitize the signals output by the thermocouples 116a-i. First through third current sensing lines 408a-c electrically connect three of the processor's 402 input pins to the series elements 406a-c. More particularly, first through third current sensing lines 408a-c are electrically connected directly to the end of the resistive load 110 of the first through third series elements 406a-c, respectively, that is opposite the transistor 112. When the transistor 112 for any of the series elements 406a-c is on, the current sensing line 408a-c directly connected to that element 406a-c permits the processor 402 to measure the voltage across the resistive load 110 of that element 406a-c, which permits the processor 402 to determine the current flowing through the resistive load 110 using Ohm's Law.
While the thermocouples 116a-i are directly connected to the processor 402 in
A flowchart of one example method 500 for inhibiting thermal runaway that may be encoded on to the computer readable medium 404 is shown in
If the processor 402 determines at block 506 that the battery cell has not exceeded 120° C., it proceeds to block 510 where it determines whether the battery cell is between 70° C. and 120° C. If yes, the processor 402 proceeds to block 511 where it determines whether the SOC of the battery cell is above 50%. If yes, the processor 402 proceeds to block 512 where it decreases the SOC of the battery cell to a safe SOC, which when the measured temperature is between 70° C. and 120° C. is 50%. Reducing the SOC to 50% inhibits the battery cell's progression to its self-heating temperature. Following reducing the SOC, the processor 402 proceeds to block 520 where the method 500 ends. 70° C. in this example is a warning temperature that indicates the battery cell is operating significantly above its normal operating temperature, notwithstanding that it has not yet reached its self-heating temperature. Alternatively, if at block 511 the processor 402 determines that the battery cell's SOC is below 50%, the processor 402 bypasses block 512 and ends the method 500 by proceeding directly to block 520.
If the processor 402 determines at block 510 that the battery cell has not exceeded 70° C., it proceeds to block 514 where it determines whether the battery cell is between 60° C. and 70° C. If yes, the processor 402 proceeds to block 515 where it determines whether the SOC of the battery cell is above 70%. If yes, the processor 402 proceeds to block 516 where it decreases the SOC of the battery cell to a safe SOC, which when the measured temperature is between 60° C. and 70° C. is 70%. Reducing the SOC to 70% inhibits the battery cell's progression to its self-heating temperature. Following reducing the SOC, the processor 402 proceeds to block 520 where the method 500 ends. In this example, 60° C. is the maximum normal operating temperature of the battery cell, and the battery cell's exceeding its maximum normal operating temperature may be a precursor to thermal runaway notwithstanding the risk is not yet as high as when the battery cell is at the warning or self-heating temperatures. Alternatively, if at block 515 the processor 402 determines that the battery cell's SOC is below 70%, the processor 402 bypasses block 516 and ends the method 500 by proceeding directly to block 520.
If the processor 402 determines at block 514 that the battery cell has not exceeds 60° C., then the battery cell's temperature is not indicative of potential or imminent self-heating or thermal runaway. The processor 402 accordingly proceeds to block 518 where it maintains normal operation of the battery cell, following which it proceeds to block 520 where the method 500 ends.
While in
Referring now to
Each of the PTCs 118a-qq is contained within the packaging of one of the battery cells 604a-qq and comprises first and second terminals: its first terminal is electrically connected in series to a negative terminal of one of the voltage sources 102a-qq, and its second terminal is connected to the second terminals of each of the other PTCs 118a-qq, which are thereby commonly connected together and connected to one of the terminals 108 of the battery pack 600. The effect of positioning each of the PTCs 118a-qq within the packaging of one of the battery cells 604a-qq is that should any of the PTCs 118a-qq transition to their high impedance state as a result of a temperature increase, the voltage sources 102a-qq to which those tripped PTCs 118a-qq are connected in series will be electrically isolated from all the other voltage sources 102a-qq in the battery pack 600. This limits the amount of energy that can be used to fuel a thermal runaway and decreases the rates at which one or both of the battery cells' 604a-qq temperatures and pressures increase.
In the embodiment of
The processor 402 used in the foregoing embodiments may be, for example, a microprocessor, microcontroller, programmable logic controller, field programmable gate array, or an application-specific integrated circuit. Examples of the computer readable medium 404 are non-transitory and include disc-based media such as CD-ROMs and DVDs, magnetic media such as hard drives and other forms of magnetic disk storage, semiconductor based media such as flash media, random access memory, and read only memory.
For the sake of convenience, the example embodiments above are described as various interconnected functional blocks or distinct software modules. This is not necessary, however, and there may be cases where these functional blocks or modules are equivalently aggregated into a single logic device, program or operation with unclear boundaries. In any event, the functional blocks and software modules or features of the flexible interface can be implemented by themselves, or in combination with other operations in either hardware or software.
It is contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification.
While particular embodiments have been described in the foregoing, it is to be understood that other embodiments are possible and are intended to be included herein. It will be clear to any person skilled in the art that modifications of and adjustments to the foregoing embodiments, not shown, are possible.
Filing Document | Filing Date | Country | Kind |
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PCT/CA2015/050275 | 4/2/2015 | WO | 00 |
Number | Date | Country | |
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61974316 | Apr 2014 | US |