Patent Publication Number: US-2019190101-A1

Title: Fast thermal dumping for batteries

Description:
If an Application Data Sheet (ADS) has been filed on the filing date of this application, it is incorporated by reference herein. Any applications claimed on the ADS for priority under 35 U.S.C. §§ 119, 120, 121, or 365(c), and any and all parent, grandparent, great-grandparent, etc. applications of such applications, are also incorporated by reference, including any priority claims made in those applications and any material incorporated by reference, to the extent such subject matter is not inconsistent herewith. 
     SUMMARY 
     In one aspect, a system for cooling thermal runaway in a batter includes a fluid delivery system configured to transport a working liquid (e.g., water, a CFC, an HFC, an HCFC, a BCFC, or a mixture thereof) into thermal contact with the battery and further configured to permit the working liquid to vaporize to form an exhaust gas, and an exhaust system configured to vent the exhaust gas. The system may include a storage tank for the working liquid, and may be configured to work without a connection to an external source of working liquid. The system may include a structure configured to route the working liquid through the battery interior, for example multiple channels that bring working liquid through a plurality of locations within the battery. These may be configured to cool the battery at different cooling rates in different locations, for example separately controlling the cooling rate of each cell of a multi-cell battery. The fluid delivery system may include a pump, a valve, or a pressurization source (e.g., a source pressurized by a portion of the exhaust gas). The system may further include triggering circuitry configured to activate the cooling system in response to a battery condition (e.g., temperature, current, rate of change of temperature, acceleration, acceleration history, speed, speed history, internal pressure of the battery, or structural integrity of the battery), and optionally a memory configured to store a record of the battery condition or a record of the cooling system activation. The system may include a heat transfer structure (e.g., including a heat pipe, a coolant flow conduit, or a thermal conductor) configured to transport heat from the interior of the battery to an external heat exchanger, where the fluid delivery system is configured to route the working liquid into thermal contact with the external heat exchanger. The system may include triggering circuitry configured to activate the cooling system in response to an external command, or flow rate circuitry configured to control a flow rate of the working liquid within the fluid delivery system in response to a battery condition (e.g., battery temperature profile). The system may be configured to deliver working liquid to different cells of the battery at different rates. 
     In another aspect, a method of cooling a battery includes bringing a working liquid (e.g., water, a CFC, an HFC, an HCFC, a BCFC, or a mixture thereof) into thermal contact with the battery, allowing the working liquid to vaporize to form an exhaust gas, and venting the exhaust gas. The method may include storing the working liquid the working liquid in a storage tank, and bringing it from the tank without an existing connection to an external liquid supply. The method may include routing the working liquid through the battery interior, for example via multiple channels that bring working liquid to a plurality of locations within the battery. These may be configured to cool the battery at different cooling rates in different locations, for example separately controlling the cooling rate of each cell of a multi-cell battery. The method may include pumping the working liquid. The method may further include activating the cooling system in response to a battery condition (e.g., temperature, current, rate of change of temperature, acceleration, acceleration history, speed, speed history, internal pressure of the battery, or structural integrity of the battery), and optionally storing a record of the battery condition or a record of the cooling system activation in a memory. The method may include transporting heat via a heat transfer structure (e.g., a heat pipe, a coolant flow conduit, or a thermal conductor) from the interior of the battery to an external heat exchanger, and placing the working liquid into thermal contact with the external heat exchanger. The method may include activating the cooling system in response to an external command, or adjusting a flow rate of the working liquid within the fluid delivery system in response to a battery condition (e.g., battery temperature profile). The method may include delivering working liquid to different cells of the battery at different rates. 
     In still another aspect, a system for cooling a battery includes means for bringing a working liquid (e.g., water, a CFC, an HFC, an HCFC, a BCFC, or a mixture thereof) into thermal contact with the battery, means for allowing the working liquid to vaporize to form an exhaust gas, and means for venting the exhaust gas. The system may include a storage tank that stores the working liquid, and means for bringing it from the tank without an existing connection to an external liquid supply. The system may include means for routing the working liquid through the battery interior, for example via multiple channels that bring working liquid to a plurality of locations within the battery. These may be configured to cool the battery at different cooling rates in different locations, for example separately controlling the cooling rate of each cell of a multi-cell battery. The means for bringing the working liquid into thermal contact with at least a portion of the battery may include a pump, a valve, or a pressurization source. The system may further include means for activating the cooling system in response to a battery condition (e.g., temperature, current, rate of change of temperature, acceleration, acceleration history, speed, speed history, internal pressure of the battery, or structural integrity of the battery), and optionally means for storing a record of the battery condition or a record of the cooling system activation in a memory. The system may include means for transporting heat via a heat transfer structure (e.g., a heat pipe, a coolant flow conduit, or a thermal conductor) from the interior of the battery to an external heat exchanger, and means for placing the working liquid into thermal contact with the external heat exchanger. The system may include means for activating the cooling system in response to an external command, or means for adjusting a flow rate of the working liquid within the fluid delivery system in response to a battery condition (e.g., battery temperature profile). The system may include means for delivering working liquid to different cells of the battery at different rates. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a battery cooling system. 
         FIG. 2  is a flow chart of a method of operating the battery cooling system of  FIG. 1 . 
         FIG. 3  is a detail of a battery having separate flow control in different cells. 
         FIG. 4  is a detail of a battery having valves to control routing of exhaust gas. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. 
     The term “circulated,” as it is used herein, includes flowing a fluid through a pipe, channel, or conduit, or through an indeterminate path such as through an open-cell foam, either once or multiple times. The term “recirculated,” as it is used herein, includes circulating a fluid in a configuration in which it passes through the same portion of an apparatus more than once. 
       FIG. 1  is a schematic drawing illustrating a cooling system for a battery  100 , such as an auto battery. Battery  100  includes multiple cells  102 , each with a positive and negative terminal as shown. Cells  102  are wired in parallel and connected to positive and negative battery terminals  104  in a conventional manner. A fluid delivery system includes reservoir  106 , pump  108 , heat exchanger pipes  110 , and exhaust  112 . Reservoir  106  holds a working liquid  114 . Any convenient working liquid that may be circulated through the battery at its working temperature and that may be vaporized as described below may be used. It is expected that water will represent a good working liquid in many embodiments, since it has a relatively high heat of vaporization and is innocuous when vented to the atmosphere, but in some embodiments, more exotic working liquids may be appropriate, such as chlorofluorocarbons (CFCs, e.g., FREON™), hydrofluorocarbons (HFCs), hydrofluorochlorocarbons (HCFCs), bromochlorofluorocarbons (BCFCs), or mixtures of any of the preceding compounds, which may, for example, be azeotropic mixtures. 
     Heat exchanger pipes  110  are provided that allow working liquid  114  from reservoir  106  to be circulated through the battery, either by free convection or assisted by one or more pumps  108 . (One pump is illustrated in  FIG. 1 , but in other embodiments, pumps  108  may be provided throughout the system, which may be jointly or separately controlled, as further discussed below in connection with  FIG. 3 . Alternatively, instead of a pump, the system may harness pressure generated by vaporization of working fluid  114  or the energy of a catastrophic event precipitating rapid cooling, as further discussed below.) In the embodiment shown in  FIG. 1 , the system includes defined pipes in thermal communication with the battery cells  102 , but in other embodiments, fluid may be circulated around or even through the cells in any convenient configuration. For example, cells  102  may be embedded in an open-cell foam through which the working liquid  114  circulates, or there are may be perforations in cells  102  that are designed to permit working fluid  114  to exchange heat with cells  102  without unacceptably degrading the electrical performance of the cells. In some embodiments, solid heat pipes or similar structures (not shown) conduct heat out of the cells to the heat exchanger pipes  110 . The illustrated heat exchanger pipes  110  are connected to exhaust  112  that allows vaporized working liquid to be vented, for example to the atmosphere or to a sealed balloon or the like (not shown) where it can be subsequently harvested for reuse. 
       FIG. 2  is a flow chart illustrating steps of one method of using the cooling system illustrated in  FIG. 1 . In normal operation, working liquid  114  circulates  202  through battery  100  to cool it, either through free convection or assisted by pump  108 . However, upon experiencing a precipitating event  204 , system  100  shifts to an irreversible cooling mode designed to cool the battery as fast as possible, before thermal runaway can occur. In some embodiments, precipitating events may include temperature exceeding a threshold, rate of temperature change exceeding a threshold, rapid acceleration of the system (e.g., an impact), internal pressure of the battery, compromise of the integrity of one or more cells  102 , or a received command such as a wireless command. In the embodiment shown in  FIG. 1 , working liquid  114  is pumped through the system by pump(s)  108  to cool the battery  206 , and is allowed to vaporize  208  to absorb as much heat as possible via evaporative cooling, and is vented to the atmosphere through exhaust  112 . 
       FIG. 3  is a schematic showing the interior of a battery equipped to individually control the cooling rate for each cell. Each cell  302  has an associated heat exchanger pipe  310 , each with its own pump  308 . The schematic illustration shows each heat exchanger pipe  310  as a loop around cell  302 , but it will be understood that the path of each pipe  310  may vary from this configuration, and should be designed to efficiently remove heat from cell  302 . Thermocouple  304  is positioned to measure the temperature of cell  302 , and to provide a feedback signal to pump  308 . The speed of pump  308  is controlled relative to the temperature measured by thermocouple  304  so that cell  302  is cooled at a controlled rate, which can be independently controlled for each cell  302 . For example, more cooling may be needed for cells in the center of the battery than for cells at the periphery. 
     Thermocouple  304  and pump  308  may also be connected to circuitry for measuring and recording the temperature and cooling rate of the battery. In some embodiments, such a record may include time-stamping or place-stamping (e.g., via GPS), so that the performance of the battery can be reconstructed, for example for forensic purposes after an accident. 
     In other embodiments, rather than directly routing the working liquid through the battery, the battery may include thermal conductors (heat pipes) configured to transport heat to a heat exchanger. In some embodiments, a single or a few heat pipes may serve the whole battery, which is others, individual heat pipes may be provided for each cell or other region of the battery interior. In embodiments in which heat pipes are provided to transport heat to a heat exchanger, the working liquid is brought into thermal contact with the heat pipes, which in some embodiments may be outside of the main battery compartment. Those of skill in the art will recognize that this design may facilitate the construction of batteries that need not be able to tolerate working liquid in the battery interior, but that this advantage must be balanced against possible inefficiencies in transporting heat to the working liquid (instead of transporting the working liquid to the heat source). 
     Pressures generated by vaporization of a working liquid in a battery can be quite high if the fluid is not adequately vented. Plumbing in the battery should generally be designed with an eye to managing pressures to avoid rupturing a heat exchanger pipe within the battery, although in some embodiments, planned rupture may be used to improve heat transfer within the battery. However, such pressures can also be leveraged to increase fluid flow, in some embodiments even to the point where pump  108  can be omitted from the system. In some embodiments, liquid recirculates around the battery (with or without a pump), until the cooling system is activated (for example, by a substantial temperature excursion within the battery, or by a detected rapid deceleration indicative of an impact). 
       FIG. 4  shows an exhaust system that uses internal pressure to reroute the path of the exhaust gas. Working liquid  414  is stored in reservoir  406  and circulated through battery  416 , absorbing heat from the battery and vaporizing to form exhaust gas. Exhaust port  418  for the vaporized exhaust gas leads to a chamber  420  having two one-way, pressure activated, valves. Recirculation valve  422  opens at a first pressure P 1 , thereby allowing pressurization of the reservoir  406 . If the pressure reaches a greater pressure P 2 , exhaust valve  424  opens, allowing excess exhaust gas to be vented through exhaust pipe  412 . 
     While the novel batteries presented herein may be used in stationary applications, they are particularly well-suited for use in vehicles or other devices that move independently (e.g., robots or autonomous vehicles). In such embodiments, the vehicle or other device typically carries a tank of working liquid that may be vented in the case of a battery failure. For example, currently used electric vehicle batteries usually store about 15-60 kW-h of electrochemical energy. Water absorbs about 2.3 kJ/g when vaporized, so it would require about 22-87 kg of water to be vaporized to dissipate all of the electrochemical energy in the battery (neglecting energy used to heat the water to the boiling point and any possible parasitic losses), a reasonable amount to carry with the battery in a dedicated storage tank or the like (22 kg of water occupies less than a cubic foot of space). (Dichlorodifluoromethane (FREON-12) is much less efficient with a latent heat of vaporization of 0.17 kJ/g, but may nevertheless be preferable in some embodiments.) Those of skill in the art will understand that these numbers are estimates used to demonstrate feasibility of the concept and are not intended to be limiting. In some embodiments, slower cooling or incomplete cooling may be tolerable, in which case less working liquid may be carried. In other embodiments, speed of cooling may be paramount, in which case pumping must be faster and thermal transfer to the working liquid made as efficient as possible to optimize performance. 
     Various embodiments of electrochemical devices and methods have been described herein. In general, features that have been described in connection with one particular embodiment may be used in other embodiments, unless context dictates otherwise. For example, the individual cell cooling described in connection with  FIG. 3  may be employed in the devices described in connection with  FIG. 4 , or with any of the embodiments described herein. For the sake of brevity, descriptions of such features have not been repeated, but will be understood to be included in the different aspects and embodiments described herein. 
     It will be understood that, in general, terms used herein, and especially in the appended claims, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of introductory phrases such as “at least one” or “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a cell” should typically be interpreted to mean “at least one cell”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, it will be recognized that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two heat pipes,” or “a plurality of heat pipes,” without other modifiers, typically means at least two heat pipes). Furthermore, in those instances where a phrase such as “at least one of A, B, and C,” “at least one of A, B, or C,” or “an [item] selected from the group consisting of A, B, and C,” is used, in general such a construction is intended to be disjunctive (e.g., any of these phrases would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, and may further include more than one of A, B, or C, such as A 1 , A 2 , and C together, A, B 1 , B 2 , C 1 , and C 2  together, or B 1  and B 2  together). It will be further understood that virtually any disjunctive word or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.