Patent Publication Number: US-2017365895-A1

Title: Energy storage system with heat pipe thermal management

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present U.S. Utility patent application claims priority pursuant to 35 U.S.C. §120 as a continuation of U.S. Utility application Ser. No. 14/189,219 entitled “ENERGY STORAGE SYSTEM WITH HEAT PIPE THERMAL MANAGEMENT”, filed 25 Feb. 2014, which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility patent application for all purposes. 
    
    
     BACKGROUND 
     Energy storage systems are used in a variety of contexts. For example, an electric vehicle can have a number of individual energy storage units (e.g., lithium-ion cells) stored inside a compartment, and this system is often referred to as a battery pack. Cells and other storage units generate heat during operation, such as during the charging process and when the cells are used to deliver energy, for example to the propulsion/traction system of the vehicle. 
     One cooling approach currently being used involves lithium-ion cells that are electrically connected by an anode terminal at the bottom of the cell, and a cathode terminal on top of the cell. These cells are arranged to all have the same orientation (e.g., “standing up”) with some spacing provided between all adjacent cells. The spacing facilitates a cooling conduit to run between the cells and be in contact with at least a portion of the outer surface of each cell. The cooling conduit has a coolant flowing through it, which removes thermal energy from inside the battery pack to some location on the outside, where heat can be safely dissipated. In order to provide a safe coolant flow, one must provide fluid connections into and out of the battery package, and the coolant path inside the battery pack must be reliable and have enough capacity. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an example of an assembly that is part of an energy storage system. 
         FIG. 2  shows an example of an energy storage system with heat pipes that have an L-shape. 
         FIG. 3  shows another example of an energy storage system with heat pipes that have an L-shape. 
         FIG. 4  shows an example of an energy storage system with heat pipes that have a U-shape. 
         FIG. 5  shows another example of an energy storage system with heat pipes that have a U-shape. 
         FIG. 6  shows another example of an energy storage system with one or more heat pipes that have a U-shape, also including coolant tubes. 
         FIG. 7  shows an example of an energy storage system with linear heat pipes. 
         FIG. 8  shows another example of an energy storage system with the linear heat pipes from  FIG. 7 . 
         FIG. 9  shows an example of an energy storage system where heat pipes have a deformation corresponding to a cross section profile of a heat transfer channel. 
         FIG. 10  shows another example of an energy storage system with heat pipes having a U-shape, with thermal tubes on top and bottom. 
         FIG. 11  shows another example of an energy storage system with heat pipes having a U-shape, with thermal tubes extending between manifolds positioned at shorter sides of the system. 
         FIG. 11A  is a cross section of the energy storage system in  FIG. 11 . 
         FIG. 12  shows another example of an energy storage system with heat pipes having a U-shape, with thermal tubes extending between manifolds positioned at longer sides of the system. 
         FIG. 12A  is a cross section of the energy storage system in  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     This document describes examples of systems and techniques that provide face cooling of cells or other energy storage units by way of heat pipes. This can provide useful advantages, such as: The need for internal fluid connections in a battery pack can be eliminated, thereby avoiding leakage; a closed loop cooling system can be provided that reduces pressure drop losses with regard to an overall cooling system (e.g., in a vehicle); external cooling tube assemblies can be eliminated; rapid fluid migration can be provided that keeps cells at even temperatures; cooling tube sections between rows of cells can be eliminated, thereby allowing more cells to be packed into a given space; and even if a rupture occurs in one of the heat pipe lumens, significant cooling/heating can nevertheless be provided by way of other undamaged lumens within the heat pipe. 
       FIG. 1  shows an example of an assembly  100  that is part of an energy storage system. Particularly, the energy storage system contains an interconnected array of energy storage elements, two cells  102  of which are shown here. In this example, the cells are physically secured and held in place (e.g., to a particular torque value) by a pair of opposing clamshells: a top clamshell  104  and a bottom clamshell  106 . For example, the clamshells have openings exposing the respective ends of each cell. In other implementations, the cells can be secured by a different technique, such as by a structure interleaved between cells. 
     Here, a flexible printed circuit  108  overlies and connects electrical terminals of the cells  102 . In this implementation, the flexible printed circuit includes three layers: a flexible conductive layer  110  sandwiched between a flexible bottom insulating layer  112  and a flexible top insulating layer  114 . The conducting layer can be a uniform layer of metal, such as copper, and the insulating layers can be uniform layers of polyimide (e.g., a Kapton® material). In other implementations, one or more other materials can be used in lieu of or in combination with the mentioned materials. 
     Here, the cells  102  are a type of rechargeable battery cell having a flat top with terminals at one end. Particularly, each cell has a center positive terminal  116  and a surrounding annular negative terminal  118 . For example, the annular negative terminal can be part of, or mounted on, a main housing of the cell (e.g., the cell can) that extends along the length of the cell and forms the other end of the cell (i.e., the bottom end in this example). 
     The patterning of flexible printed circuit  108  produces die cut areas  120  in the bottom insulating layer  112  to allow exposed portions of conductive layer  110  to make electrical contact, for example to selectively connect to the terminals of the cell(s). Here, die cut areas  122  in top insulating layer  114  allow exposed portions of conductive layer  110  to receive a device that produces an electromechanical connection between the portion of conductive layer interacting with the device and the underlying surface to be joined (e.g., a terminal of one of the cells  102 ). Any of several different types of devices and techniques can be used in making the electromechanical joints. For example, spot welds  124  here join portions of the conductive layer  110  to respective terminals of the individual cells. 
     The energy storage system can be implemented as a source of propulsion energy in an electric vehicle, to name just one example. That is, a number of cells can be interconnected in the energy storage system to form an array (e.g., a battery pack) that powers the vehicle. In other implementations, the illustrated assembly can also or instead power another aspect of a vehicle, or can be used in a non-vehicle context, such as in a stationary storage. 
     In the illustrated embodiment, the cells  102  are oriented vertically, and are shown standing on a heat pipe  126 . The heat pipe can be connected to a thermal management system (not shown) to provide for thermal management of the energy storage system. Cooling of the cells  102  can be performed using an evaporation end  126 A that faces the cells, and at least one condensation end  126 B. The evaporation end can extend for at least the entire length required by the array of cells, or part thereof. Here, the heat pipe  126  has an L-shape when viewed from the side, with the condensation end elevated above the evaporation end. In other implementations, the heat pipe can have a different shape. For example, and without limitation, more than one condensation end can be provided. In some implementations, the heat pipe can instead provide heating of the cells and the rest of the energy storage system. 
     In this example, the assembly  100  has an electric insulator layer  128  between the evaporation end  126 A of the heat pipe  126  and the bottom of the cells  102 . This layer prevents electric contact between the heat pipe (which can be a metal component) and the cell housing. For example, a thermal interface material (TIM) can be used to electrically insulate an anode terminal at the bottom of the cell while allowing cooling/heating of the cells through the same surface. In some implementations, the assembly is manufactured by applying the electric insulator layer on the heat pipe, applying adhesive onto the top of the layer (e.g., at each cell position), and then positioning the cell or cells on the layer. 
     The heat pipe can be manufactured from any suitable material. In some implementations, the heat pipe can be extruded from metal and have at least one interior channel for the phase-change fluid. The interior channel(s) can have one or more features that aid the flow of fluid in the liquid phase and/or gas phase. For example, a groove, powder and/or sponge can be provided inside the heat pipe. 
       FIG. 2  shows an example of an energy storage system  200  with heat pipes  202  that have an L-shape. In this example, an evaporation surface  202 A is oriented essentially horizontally (e.g., inside a battery pack of an electric vehicle) and a condensation surface  202 B is oriented essentially vertically. A module  204  of cells (e.g., lithium-ion cells of the 18650 type) is here shown positioned on one of the heat pipes. The interface between the module and the heat pipe is by conductive thermal contact requiring a TIM. For example, the heat pipe can comprise multiple adjacent parallel heat sections attached to each other (e.g., by welding). The module can have more or fewer cells than illustrated in this example, and/or the cells can be arranged in a different configuration. For clarity, only one module of cells is shown here. Implementations of energy storage systems can have any number of modules. 
     The energy storage system  200  has at least one heat transfer channel  206  that is in thermal exchange with the heat pipes  202 . In some implementations, an auxiliary system can circulate fluid, such as coolant, in one or more channels inside the heat transfer channel. For example, the energy storage system described here can be incorporated as a battery pack in an electric (or hybrid) vehicle, and a cooling system external to the battery pack can then cool the fluid from the heat transfer channel, thereby removing heat from the cells. 
     Here, the heat transfer channel  206  is provided in the middle of the energy storage system  200 , and the module  204  and other modules can then be positioned in rows on each side of the channel, for example in a location  208 . The condensation ends/surfaces of the respective heat pipes are here positioned so that they about the sides of the heat transfer channel. Accordingly, the heat pipes extend from the channel in opposite directions. Here, the heat pipe  202  on which the module  204  is positioned is shown to consist of six parallel heat pipe sections. Solely as an example, each of such sections can contain 14 separate internal channels, each of which individually operates according to the principle of a heat pipe. 
       FIG. 3  shows another example of an energy storage system  300  with heat pipes  302  that have an L-shape. Each of the heat pipes has a module  304  of cells associated with it. The cells are aligned with each other so that one of their ends (e.g., the bottom end, or a negative end) faces an evaporation surface  302 A of the heat pipe. In this implementation, the cells are positioned essentially horizontally and the evaporation surface is vertical. A condensation surface  302 B of the heat pipe, however, is elevated above the evaporation surface and is horizontal in this example. In some implementations, a cooling surface can be formed by all the condensation surfaces collectively, or can be a separate surface applied on top of them. Such a cooling surface can then be used for removing heat from all of the cell modules. For example, the cooling surface can be provided with a common active cooling channel (analogous to the heat transfer channel  206  of  FIG. 2 ); heat spreaders transverse to the cooling channel can then accumulate heat from the respective condensation surfaces and transport that heat to the cooling channel. 
       FIG. 4  shows an example of an energy storage system  400  with heat pipes  402  that have a U-shape. That is, each of the heat pipes has an evaporation surface  402 A and two condensation surfaces  402 B, one at either end of the evaporation surface. Each of the heat pipes has a module  404  of cells associated with it. For example, this system can be useful in a vehicle, because the U-shaped heat pipes provide increased independence from angularity changes (e.g., when the vehicle is operating on an inclined and/or graded surface). 
     The energy storage system has a central heat transfer channel  406  and one or more side heat transfer channels  408 , each of which is in thermal exchange with the heat pipes  402 . Here, the side heat transfer channels are provided at the ends of the heat pipes opposite the central heat transfer channel. In this implementation, the heat pipes are oriented along the length of the modules  404 . For example, this energy storage system can provide an advantageously small ratio of condensation area relative to evaporation area, which allows the cooling tube to occupy a relatively small volume of the battery pack. 
       FIG. 5  shows another example of an energy storage system  500  with heat pipes  502  that have a U-shape. Each of the heat pipes has an evaporation surface  502 A and two condensation surfaces  502 B, one at either end of the evaporation surface. Each of the heat pipes has a module  504  of cells associated with it. The energy storage system has a central heat transfer channel  506  and one or more cross member heat transfer channels  508 , each of which is in thermal exchange with the heat pipes  502 . The cross member heat transfer channels are transverse to the central channel; for example, the cross member can extend equally far on both sides thereof. A heat transfer medium (e.g., coolant) can flow in the heat transfer channels to provide thermal exchange with the heat pipes. Here, the heat pipes are oriented across the width of each battery module. For example, this energy storage system can provide an advantageously small ratio of condensation area relative to evaporation area. 
       FIG. 6  shows another example of an energy storage system  600  with one or more heat pipes  602  that have a U-shape, also including coolant tubes  604 . Each of the heat pipes has an evaporation surface  602 A and two condensation surfaces  602 B, one at either end of the evaporation surface. This example shows a module  606  of cells in the energy storage system. For example, during operation the heat pipe can convey heat in both directions along the evaporation surface, towards each respective condensation surface. That is, the thermal flow inside the heat pipe is here parallel to the plane of this drawing. 
     This energy storage system also has the coolant tubes  604  that are in thermal exchange with the heat pipes  602 . In this example, each of the coolant tubes has an essentially L-shaped profile. For example, the profile of the L-shape can at least partially correspond to the outer surface of the U-shaped heat pipe. This provides an advantageously large surface area of contact between the coolant tube and the heat pipe, which facilitates thermal exchange between them. The coolant tubes  604  can provide reversibility (i.e., the ability to do both heating and cooling) of the heat pipe. For example, the L-shaped profile of the coolant tubes facilitates removal of heat from the evaporation surface  602 A during cooling of the module, and also delivery of heat from the condensation surfaces  602 B to the module during heating. As another example, the shape and configuration of the system in this example can help reduce gravitational issues that might otherwise occur, such as if the grooves of the heat pipe are not manufactured to give effective capillary force. This configuration can also improve the way that the U-shaped heat pipe is packaged inside a housing or other structure that holds the energy storage system. 
     The coolant tube has one or more interior channels in which coolant can be circulated within the system (i.e., the coolant can flow in directions into, and out of, the plane of the figure). The two coolant tubes in this example can have coolant flowing in the opposite, or the same, direction as each other. In some implementations, the coolant tube can be used for providing reversible thermal transfer, such that the energy storage system can be cooled or heated depending on what is needed. For example, the condenser contact here extends onto the flat portion of the heat pipe and can therefore also be used for delivering heat (e.g., from an external heating system) into the heat pipe, from where the heat then flows into the individual cells. 
       FIG. 7  shows an example of an energy storage system  700  with linear heat pipes  702 . Each of the heat pipes has a module  704  of cells associated with it. The energy storage system has a central heat transfer channel  706  that can have coolant flowing through it. Here, an end portion  702 A of each heat pipe serves as an evaporation area, and a central portion  702 B of the heat pipe (i.e., near the heat transfer channel) serves as a condensation area. The internal channel(s) of the heat pipe can be truncated at the central heat transfer channel, or can extend along the length of the heat pipe. This energy storage system can provide a relatively large ratio of evaporation area relative to condensation area, and can work reversibly (i.e., to provide heating instead of cooling). Also, this implementation can be efficient in terms of volumetric energy density. 
       FIG. 8  shows another example of an energy storage system  800  with the linear heat pipes  702  from  FIG. 7 . The system here also has the module  704  of cells, and the central heat transfer channel  706 . In addition, the system has one or more side heat transfer channels  802  through which coolant can flow. For example, the side channel(s) can be positioned at the ends of the heat pipes. This system can be useful in a vehicle, because the positions of the central and side heat transfer channels provide increased independence from angularity changes (e.g., when operating the vehicle on an inclined and/or graded surface). As another example, the system can provide reversible heat transfer, such as for heating the cells instead of cooling them. 
       FIG. 9  shows an example of an energy storage system  900  where heat pipes  902  have a deformation  904  corresponding to a cross section profile of a heat transfer channel  906 . That is, while the heat pipes are here generally linear in areas where the battery cell modules are located, the heat pipe here has the deformation so as to conform a condensation end of the heat pipe to the shape of the heat transfer channel. The internal channel(s) of the heat pipe can be truncated at the central heat transfer channel, or can extend along the length of the heat pipe. For example, this system can provide a smaller ratio of condensation area relative to evaporation area than a corresponding L-shape heat pipe. 
       FIG. 10  shows another example of an energy storage system  1000  with heat pipes  1002  having a U-shape, with thermal tubes on top and bottom. Each heat pipe encloses a module  1004  of cells, only one of which modules is shown here for simplicity. The heat pipes are organized so that the system has four heat pipes across its width, and three (sets of four) heat pipes along its length. Other configurations and/or numbers of heat pipes can be used in other implementations. For example, and without limitation, the energy storage system could have a width of one heat pipe. In yet another implementation, one or more heat pipes can instead be transverse to the length of the energy storage system. 
     Here, the energy storage system  1000  is arranged so that the larger surface of the heat pipes—i.e., the one abutting the non-terminal ends of the cells—is generally vertical. The two opposing heat pipe surfaces—which abut the side surfaces of the outermost rows of cells—are generally horizontal. 
     Thermal tubes  1006  and  1008  are placed on the top and bottom of the heat pipes, respectively. Each thermal tube is manufactured of a material with sufficient thermal conductivity to absorb heat from, or deliver heat into, the heat pipes through the facing surface. For example, the thermal tube can have a number of internal channels configured for having a fluid (e.g., coolant) flowing therein. As such, the thermal tubes can be connected to an external cooling/heating system (not shown), which can be located outside the housing of the energy storage system. 
     As a first example, both the thermal tubes  1006  and  1008  can be used for cooling the cells of the energy storage system by way of a flowing coolant. In some implementations, coolant flows in opposite directions in the two respective thermal tubes. 
     As a second example, the thermal tube  1006  (i.e., on top) can be used for cooling the cells, and the thermal tube  1008  (i.e., on the bottom) can be used for heating the cells. This configuration is advantageous in that the heat pipe operates aided by gravity, rather than against gravity, and is more efficient as a result. In a normally vertical heat pipe section the vapor will always move upward unless the vehicle orientation is rotated by at least 90 degrees. The above advantage can therefore be relatively unaffected by vehicle orientation. Both when the batteries are being cooled and when they are being heated, the less dense vapor will move upward (opposite to gravity) and the fluid will move downward (with gravity). That is, during operation, when the cells (and/or other electrical devices in the system) are generating heat, the upper thermal tube can serve to cool the system by way of removing thermal energy from the heat pipes. In contrast, when the cells (and/or the rest of the energy storage system) need to be warmed up, such as before operating the system in a cold environment, the lower thermal tube can serve to warm the system by way of introducing thermal energy into the heat pipes. For example, the flow of cooling/heating fluid can be directed to either the upper or lower thermal tube, as applicable, by way of a valve, such as a solenoid valve. 
       FIG. 11  shows another example of an energy storage system  1100  with heat pipes  1102  having a U-shape, with thermal tubes  1104  extending between manifolds  1106  and  1108  positioned at shorter sides of the system. The heat pipes hold modules of cells adjacent the thermal tubes, of which only modules  1110  and  1112  of cells are shown for clarity. That is, in this example the thermal tubes are parallel to the length of the energy storage system (e.g., a battery pack). 
     The manifolds  1106 - 08  and the thermal tubes  1104  have one or more channels inside them to facilitate flow of a fluid (e.g., coolant) to various parts of the system. For example, the manifold  1108  can be the inlet manifold, receiving fluid from at least one inlet  1114 , and the manifold  1106  can be the outlet manifold, with fluid exiting through at least one outlet  1116 . Between the two manifolds, the fluid passes in the interior channels of the thermal tubes  1104 , and in so doing provides thermal exchange (e.g., cooling) of the cells by way of the heat pipes. 
       FIG. 11A  is a cross section of the energy storage system in  FIG. 11 . Particularly, modules  1110  and  1112  of cells are shown positioned in heat pipes  1102 A and  1102 B, respectively. The heat pipes, in turn, are positioned between respective thermal tubes  1104 A, B and C. For example, in operation the heat from the module  1110  is conveyed by way of the heat pipe  1102 A into the thermal tubes  1104 A and B, whereas the heat from the module  1112  is conveyed by way of the heat pipe  1102 B into the thermal tubes  1104 B and C. Some configurations can have the heat pipes and/or thermal tubes arranged in other ways. 
       FIG. 12  shows another example of an energy storage system  1200  with heat pipes  1202  having a U-shape, with thermal tubes  1204  extending between manifolds  1206  and  1208  positioned at longer sides of the system. The heat pipes hold modules of cells adjacent the thermal tubes, of which only modules  1210  and  1212  of cells are shown for clarity. That is, in this example the thermal tubes are transverse to the length of the energy storage system (e.g., a battery pack). 
     The manifolds  1206 - 08  and the thermal tubes  1204  have one or more channels inside them to facilitate flow of a fluid (e.g., coolant) to various parts of the system. For example, the manifold  1208  can be the inlet manifold, receiving fluid from at least one inlet  1214 , and the manifold  1206  can be the outlet manifold, with fluid exiting through at least one outlet  1216 . Between the two manifolds, the fluid passes in the interior channels of the thermal tubes  1204 , and in so doing provides thermal exchange (e.g., cooling) of the cells by way of the heat pipes. 
       FIG. 12A  is a cross section of the energy storage system in  FIG. 12 . Particularly, modules  1210  and  1212  of cells are shown positioned in heat pipes  1202 A and  1202 B, respectively. The heat pipes, in turn, are positioned between respective thermal tubes  1204 A, B and C. For example, in operation the heat from the module  1210  is conveyed by way of the heat pipe  1202 A into the thermal tubes  1204 A and B, whereas the heat from the module  1212  is conveyed by way of the heat pipe  1202 B into the thermal tubes  1204 B and C. Some configurations can have the heat pipes and/or thermal tubes arranged in other ways. 
     As used herein, the term “heat pipe” is used in a broad sense to include a number of techniques, such as phase change thermal systems that use highly conductive materials and have a substantially flat form factor. The term heat pipe includes, but is not limited to, grooved style heat pipes, heat pins, vapor chambers, pyrolytic graphite sheets, and other technologies where heat is transferred between interfaces by way of thermal conduction and phase transition. 
     A number of implementations have been described as examples. Nevertheless, other implementations are covered by the following claims.