Patent Publication Number: US-2023143123-A1

Title: Dielectric liquid evaporative cooling for battery packs

Description:
INTRODUCTION 
     The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     The present disclosure relates to battery cooling systems, and more particularly to battery cooling systems for BEVs. 
     Battery electric vehicles (BEVs) include a battery system including one or more battery packs with one or more battery modules. Each of the battery modules includes one or more battery cells. A power control system is used to control charging and/or discharging of the battery system during operation. During driving, one or more electric motors of the BEV receive power from the battery system to provide propulsion for the vehicle and/or to return power to the battery system during regenerative braking. 
     During operation of the BEV, the battery cells may experience heating due to charging and discharging. Battery life may be adversely impacted by operation for extended periods at higher temperatures. As a result, battery cooling systems may be used to maintain the temperature of the battery system within a predetermined temperature range. For example, a normal temperature range for a lithium ion battery may be in a range from 30° C. to 50° C. 
     SUMMARY 
     A wicking assembly for battery cells of a battery cooling system includes a first face plate including vertical plate portions and horizontal plate portions defining openings. A second face plate includes vertical plate portions and horizontal plate portions defining openings. A wicking structure is made of a wicking material, defines projections on first and second outer surfaces thereof and includes a plurality of vapor escape passages. The wicking structure is configured to be sandwiched between the first face plate and the second face plate. 
     In other features, the projections on the first and second outer surfaces of the wicking structure are received in the openings of the first face plate and the second face plate, respectively. The projections on the first outer surface and the second outer surface are aligned vertically the plurality of vapor escape passages. The plurality of vapor escape passages extend in a vertical direction of the wicking structure. The wicking structure is selected from a group consisting of wire mesh and a porous material. The first and second face plates are made of a material selected from a group consisting of mica, garolite, and aerogel. 
     A battery cooling system comprises a battery enclosure, M of the wicking assembly of claim  1 , wherein M is an integer greater than one and N battery cells, where N is an integer greater than one. Each of the M wicking assemblies is arranged between adjacent ones of the N battery cells. 
     In other features, vapor manifold is defined by the battery enclosure above the N battery cells. A condenser is in fluid communication with the vapor manifold. A pump includes an inlet in fluid communication with the condenser and an outlet in fluid communication with an inlet of the battery enclosure. A separator is arranged in fluid communication between the condenser and the pump. A heat exchanger is arranged above the vapor manifold of the battery enclosure. 
     A battery cooling system comprises a battery enclosure and M wicking assemblies, where M is an integer greater than one. Each of the M wicking assemblies includes a first face plate, a second face plate and a wicking structure arranged between the first face plate and the second face plate. The battery cooling system comprises N battery cells, where N is an integer greater than one. The N battery cells comprise pouch-type battery cells. Each of the M wicking assemblies is arranged between adjacent ones of the N battery cells in the battery enclosure. 
     In other features, the first face plate includes vertical plate portions and horizontal plate portions defining openings. The second face plate includes vertical plate portions and horizontal plate portions defining openings. The wicking structure is made of a wicking material, defines projections on first and second outer surfaces thereof and includes a plurality of vapor escape passages. The projections on the first and second outer surfaces of the wicking structure are received in the openings of the first face plate and the second face plate, respectively. The projections on the first outer surface and the second outer surface are vertically aligned with the plurality of vapor escape passages. 
     In other features, the plurality of vapor escape passages extend in a vertical direction of the wicking structure. The wicking structure is selected from a group consisting of wire mesh and a porous material. The first face plate and the second face plate are made of a material selected from a group consisting of mica, garolite, and aerogel. 
     In other features, a vapor manifold defined by the battery enclosure above the N battery cells. A condenser is in fluid communication with the vapor manifold. A pump includes an inlet in fluid communication with the condenser and an outlet in fluid communication with an inlet of the battery enclosure. 
     In other features, a separator is arranged in fluid communication between the condenser and the pump. A heat exchanger is arranged above the vapor manifold of the battery enclosure. 
     A battery cooling system comprises a battery enclosure and N battery cells arranged in the battery enclosure and having a rigid outer surface, where N is an integer greater than one. Wicking material arranged on the rigid outer surface of the N battery cells. A vapor manifold is defined by the battery enclosure above the N battery cells. A condenser is in fluid communication with the vapor manifold. A pump includes an inlet in fluid communication with the condenser and an outlet in fluid communication with an inlet of the battery enclosure. 
     In other features, a separator is arranged in fluid communication between the condenser and the pump. A heat exchanger is arranged above the vapor manifold of the battery enclosure. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG.  1    is a functional block diagram of an example of a battery cooling system including a battery enclosure and wicking assemblies arranged between adjacent battery cells according to the present disclosure; 
         FIG.  2    is a side cross-sectional view illustrating an example of a battery enclosure, the battery cells and the wicking assemblies according to the present disclosure; 
         FIG.  3    is an exploded view of an example of one of the wicking assemblies including a wicking structure arranged between face plates according to the present disclosure; 
         FIG.  4    is an example of a wicking material forming part of the wicking structure according to the present disclosure; and 
         FIG.  5    is a perspective view illustrating a battery enclosure including battery cells with rigid side surfaces and a wicking material arranged around the rigid side surfaces of the battery cells. 
     
    
    
     In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
     DETAILED DESCRIPTION 
     A battery cooling system according to the present disclosure uses evaporation of dielectric fluid to cool a battery system. While the foregoing disclosure will be described in the context of a battery electric vehicle (BEV) or hybrid vehicle, the battery cooling system can be used to cool battery systems in other applications. 
     The battery cooling system performs cooling by evaporating a small amount of dielectric fluid supplied to surfaces of battery cells. In other words, a smaller amount of dielectric fluid is used instead of substantially filling a battery enclosure with dielectric fluid. In some examples, the battery enclosure requires dielectric fluid to fill under 20% (and in some cases under 10%) of a height of the battery enclosure, although higher or lower levels of dielectric fluid can be used. 
     In various examples described further below, a wicking material is used to wick dielectric fluid located in a lower portion of the battery enclosure by capillary action upwardly to allow heat exchange with side surfaces of the battery cells. The dielectric fluid absorbs heat from the side surfaces of the battery cells causing evaporation of the dielectric fluid. The vapor rises, is collected in a vapor manifold, condensed and returned by a pump to the battery enclosure. 
     The cooling action provided by the battery cooling system regulates the temperature of the battery cells. The cooling system according to the present disclosure significantly reduces the amount of coolant required for cooling, which reduces the weight of the battery cooling system and reduces energy used for pumping and required pumping capacity. 
     Referring now to  FIG.  1   , a battery cooling system  10  is shown to include a battery enclosure  20  housing a plurality of battery cells  24 . In some examples, the battery cells  24  comprise pouch-type battery cells that are generally rectangular and arranged lengthwise in a horizontal direction. The pouch-type battery cells have a non-rigid outer surface and are generally compressed in the battery enclosure. In other examples, the battery cells other battery cell formats such as cylindical, prismatic or other formats. 
     In  FIG.  1   , a cross-section of a wicking material of a wicking assembly  40  arranged between two battery cells  24  is shown to show pumping of the dielectric fluid along outer surfaces of the battery cells due to capillary action and evaporation of the dielectric fluid into vapor channels. 
     A vapor manifold  22  is located above the plurality of battery cells  24  to collect vapor exiting the vapor channels. The wicking assembly  40  includes wicking material  44  that wicks dielectric fluid  60  upwardly in  FIG.  1    along outer surfaces of the battery cells  24 . In some examples, the wicking material includes a wire mesh or a porous structure. In some examples, the wicking material is made of copper, aluminum, nickel, ceramic, stainless steel, or other suitable material. 
     As the dielectric fluid moves upwardly by capillary action of the wicking material  44  (as shown by arrows  48 ), heat from the battery cells  24  is absorbed by the dielectric fluid the dielectric fluid  60  causing evaporation. The vapor moves through vapor channels  54  (as shown by arrows  58 ) that are arranged between the wicking material  44  into the vapor manifold  22 . 
     The vaporized dielectric (arrows  58 ) flows upwardly into the vapor manifold  22 . In some examples, a heat exchanger  70  may be arranged above the vapor manifold  22  to provide additional cooling or an in-situ condensation. In some examples, the heat exchanger  70  is an air-based heat exchanger or liquid-based heat exchanger. 
     The vapor flows through conduit  74  to an inlet of a condenser  76  where the dielectric vapor is condensed back into dielectric fluid. In some examples, the condenser  76  may include a fan (not shown) to provide additional airflow. The dielectric fluid flows from an outlet of the condenser  76  through a conduit  78  to an inlet of a separator  80 . The separator  80  can be used to separate water or other impurities from the dielectric fluid. 
     An outlet of the separator  80  is connected by a conduit  82  to an inlet of a pump  84 . In some examples, Δp c +Δp pump &gt;Δp v +Δp l +p l gh where Δp c  corresponds to change in pressure due to capillary action, Δp pump  corresponds to the change in pressure of the pump, Δp v  is the vapor pressure, Δp l  is the liquid pressure, g is gravity and h is the height of the battery enclosure. 
     An outlet of the pump  84  supplies the dielectric fluid via a conduit  86  to an inlet located on a bottom portion of the battery enclosure  20 . The placement and geometry of the wicks and vapor passages are tailored based on the heat distribution of a given battery cell to provide efficient cooling. In some examples, the dielectric fluid is selected from a group consisting of 3M Novec 7000 or 7200, Chemours Vertrel XF or modified hydrocarbon-based dielectric fluids, although other dielectric fluids can be used. 
     Referring now to  FIG.  2   , a cross-sectional view of the battery enclosure  20  is shown. The battery enclosure  20  houses a plurality of battery cells  24 - 1 ,  24 - 2 , . . . ,  24 -N that are arranged adjacent to one another. Wicking assemblies  40 - 1 ,  40 - 2 , . . . ,  40 -M are arranged between adjacent pairs of the battery cells  24 - 1 ,  24 - 2 , . . . ,  24 -N. In some examples, the wicking assemblies  40 - 1 ,  40 - 2 , . . . ,  40 -M have a side cross-section that is approximately the same as the plurality of battery cells  24 - 1 ,  24 - 2 , . . . ,  24 -N. 
     Referring now to  FIG.  3   , the wicking assembly  40  includes a first face plate  110  and a second face plate  112  that sandwich a wicking structure  114  located there between. The first and second face plates  110  and  112  and the wicking structure  114  are designed to work with the applied horizontal compression used for pouch-type battery cells. 
     In some examples, the first face plate  110  and the second face plate  112  include vertical plate portions  120  that are spaced apart in a horizontal direction. Horizontal plate portions  122  extend between the vertical plate portions  120  and are also spaced apart in a vertical direction. Openings  124  are defined between the vertical plate portions  120  and the horizontal plate portions  122  of the first face plate  110  and the second face plate  112 . 
     The wicking structure  114  is made of a wicking material. In some examples, the wicking material includes a wire mesh or a porous structure. In some examples, the wicking material is made of copper, aluminum, nickel, ceramic, stainless steel, or other suitable wicking material. The wicking structure  114  includes outer surfaces defining projections  134 . The projections  134  extend outwardly and are received by the openings  124  in the first face plate  110  and the second face plate  112  when the wicking assembly  40  is assembled. In some examples, the openings  124  and the projections  134  are generally rectangular, although other shapes can be used. 
     The wicking structure  114  also defines vapor escape channels  142  that extend vertically at spaced horizontal locations. In some examples, P of the projections  134  are aligned with locations of the vapor escape channels  142 , where P is an integer greater than one. In some examples, V vapor escape channels are used where V is an integer greater than one. In some examples, there are (V x P) projections on each side of the wicking structure  114 . The interleaved arrangement of the projections  134  and the openings  124  in the first and second face plates  110  and  112  prevents the vapor escape channels  142  from collapsing when compressed between the pouch-type battery cells. 
     Referring now to  FIGS.  3  and  4   , an example of the wicking material is shown further. In some examples, the wicking structure  114  is made of a wire mesh, although other types of wicking materials can be used. In  FIG.  4   , the wire mesh material including wires  90  that are interwoven to form the wire mesh. In some examples, the wicking structure  114  includes a first portion  150  and a second portion  152  having the same shape. In some examples, the first portion  150  and the second portion  152  of the wicking structure are stamped into the wire mesh, although other methods can be used. 
     The first portion  150  is mirrored relative to the second portion  152  and attached to the second portion  152  with the projections  134  facing outwardly. In some examples, the first and second face plates  110  and  112  are made of a relatively rigid material. For example, the first and second face plates  110  and  112  can be made of material selected from a group consisting of mica, garolite, and aerogel, although other materials can be used. 
     Referring now to  FIG.  5   , another battery cooling system  200  is shown to include a battery enclosure  210  including a plurality of battery cells  220 . The battery cells can include various battery cell formats such as pouch, cylindical, prismatic or other formats. In some examples, the battery cells include rigid outer surfaces (as compared to the pouch-type cells). For example, the plurality of battery cells  220  can have cylindrical or rectangular outer surfaces, although other shapes can be used. The plurality of battery cells  220  are arranged adjacent to one another in the battery enclosure  210 . A wicking material  224  is arranged around outer side surfaces of the plurality of battery cells  220 . In some examples, the wicking material  224  includes a wire mesh or a porous structure. In some examples, the wicking material is made of copper, aluminum, nickel, ceramic, stainless steel, or other suitable material. 
     Dielectric fluid  226  is located in a lower portion of the battery enclosure  210 . The wicking material  224  arranged on outer surfaces of the plurality of battery cells  220  wicks the dielectric fluid  226  upwardly against the outer surfaces of the plurality of battery cells  220  by capillary action. Heat from the plurality of battery cells  220  causes the dielectric fluid to evaporate. Vapor is collected in a vapor manifold  234 , condensed and returned to the battery enclosure  210  as described above. In some examples, the battery cooling system  200  is connected as shown in  FIG.  1   . 
     The battery cooling system according to the present disclosure provides evaporative cooling with dielectric liquid on battery cell surfaces. The battery cooling system combines evaporative cooling with dielectric liquid and external circuits for battery cooling. The wicking assembly includes wick structures, such as thin screens, to move dielectric coolant upwards along outer surfaces of the battery cells. The wicking assembly includes wick structures, such as thin screens, with additional pump assistance, to move dielectric coolant in the cooling circuit. The shape, size, and location of wicks are tailored to address uneven heat distribution of a battery cell and improve temperature uniformity. The wicking assemblies provide combined cooling and compression functions for pouch-type battery cells. 
     The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure. 
     Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” 
     In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A.