Evaporative cooling with dielectric fluid for battery packs

Abstract

Wick arrangement (40) for battery cells (24, 220) of a battery cooling system (10, 200), comprising: a first end plate (110) having vertical plate sections (120) and horizontal plate sections (122) defining openings (124); a second end plate (112) having vertical plate portions (120) and horizontal plate portions (122) defining openings (124); and a wick structure (114) made of a wick material (224) defining projections (134) on its first and second outer surfaces and containing a plurality of vapor outlet channels (142), wherein the wick structure (114) is adapted to be disposed between the first end plate (110) and the second end plate (112).

Description

[0001] The present invention relates to a wick arrangement for battery cells of a battery cooling system and to such a battery cooling system.

[0002] The information contained in this section is intended to provide a general context for the disclosure. Work by the presently named inventors, to the extent described in this section, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this disclosure.

[0003] The present disclosure relates to battery cooling systems and, more particularly, to battery cooling systems for BEVs.

[0004] Battery electric vehicles (BEVs) contain a battery system with one or more battery packs and one or more battery modules. Each battery module contains one or more battery cells. A power management system is used to control the charging and / or discharging of the battery system during operation. While driving, one or more of the BEV's electric motors receive energy from the battery system to propel the vehicle and / or return energy to the battery system during regenerative braking.

[0005] During BEV operation, the battery cells can heat up due to charging and discharging. Battery lifespan can be adversely affected by prolonged operation at higher temperatures. Therefore, battery cooling systems can be used to keep the temperature of the battery system within a specified temperature range. For example, a normal temperature range for a lithium-ion battery can be between 30°C and 50°C.

[0006] For example, the document US 2008 / 0 124 622 A1 discloses a battery pack comprising a plurality of battery modules, a plurality of holding spacers each arranged in a space between the battery modules, and first and second spacer support members that hold the holding spacers in a vertical direction, each holding spacer comprising a plurality of elastic members projecting in the vertical direction.

[0007] The document US 2010 / 0 266 883 A1 discloses a frame element for receiving a battery cell comprising an integral frame with a peripheral wall, wherein the peripheral wall has a mounting surface and an opposing cooling surface, a mounting feature located on the mounting surface, and a complementary mounting feature located on the mounting surface symmetrically opposite the mounting feature about a plane of symmetry of the frame, wherein the peripheral wall defines an opening configured to snugly receive a battery cell therein.

[0008] US 2013 / 0 108 897 A1 discloses a motor vehicle battery module comprising one or more battery cells and a heat exchanger element thermally connected to the battery cell. The heat generated in the battery cell, among other things by electrical current, can be dissipated through the heat exchanger element, which consists of a flexible substrate and one or more graphene layers arranged on the substrate.

[0009] The document US 2018 / 0 034 116 A1 discloses a battery device equipped with heat sinks for contacting the outer surfaces of a plurality of battery cells arranged within a battery casing and spacers provided adjacent to the heat sinks.

[0010] The document US 2020 / 0 136 216 A1 discloses a thermal management system for dissipating waste heat from a battery cell comprising a unit cell containing a vapor chamber with an evaporator surface and a condenser surface, wherein the evaporator surface and the condenser surface are fluidly connected by a wick. SUMMARY

[0011] It is an object of the invention to provide a more economical, lighter and more energy-efficient battery cooling system.

[0012] This problem is solved by the features of the independent claims. Advantageous further developments arise from the subclaims.

[0013] A wick assembly for battery cells of a battery cooling system includes a first end plate having vertical plate portions and horizontal plate portions defining openings. A second end plate includes vertical and horizontal plate portions defining openings. A wick structure is comprised of a wicking material, defines protrusions on its first and second outer surfaces, and includes a plurality of vapor exit channels. The wick structure is configured to be disposed between the first end plate and the second end plate.

[0014] In other features, the protrusions on the first and second outer surfaces of the wick structure are received in the openings of the first and second end plates, respectively. The protrusions on the first and second outer surfaces are vertically aligned with the plurality of vapor exit channels. The plurality of vapor exit channels extend in the vertical direction of the wick structure. The wick structure is selected from a group consisting of wire mesh and a porous material. The first and second end plates are made of a material selected from a group consisting of mica, garolite, and aerogel.

[0015] A battery cooling system comprises a battery housing, M wick assemblies according to claim 1, where M is an integer greater than one, and N battery cells, where N is an integer greater than one. Each of the M wick assemblies is disposed between adjacent ones of the N battery cells.

[0016] In other features, the vapor distributor is defined by the battery housing above the N battery cells. A condenser is in fluid communication with the vapor distributor. A pump includes an inlet in fluid communication with the condenser and an outlet in fluid communication with an inlet of the battery housing. A separator is arranged in fluid communication between the condenser and the pump. A heat exchanger is arranged above the vapor distributor of the battery housing.

[0017] A battery cooling system includes a battery case and M wick assemblies, where M is an integer greater than one. Each of the M wick assemblies includes a first end plate, a second end plate, and a wick structure disposed between the first end plate and the second end plate. The battery cooling system includes N battery cells, where N is an integer greater than one. The N battery cells include pouch battery cells. Each of the M wick assemblies is disposed between adjacent N battery cells in the battery case.

[0018] 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 wick structure is comprised of a wicking material, defines protrusions on its first and second outer surfaces, and includes a plurality of vapor exit channels. The protrusions on the first and second outer surfaces of the wick structure are received in the openings of the first and second face plates, respectively. The protrusions on the first outer surface and the second outer surface are vertically aligned with the plurality of vapor exit channels.

[0019] In other features, the plurality of vapor outlet channels extend vertically along the wick structure. The wick structure is selected from a group consisting of wire mesh and a porous material. The first end plate and the second end plate are made of a material selected from a group consisting of mica, garolite, and aerogel.

[0020] In other features, a vapor distributor is defined by the battery housing above the N battery cells. A condenser is in fluid communication with the vapor distributor. A pump includes an inlet in fluid communication with the condenser and an outlet in fluid communication with an inlet of the battery housing.

[0021] Other features include a separator in fluid communication between the condenser and the pump. A heat exchanger is located above the vapor distributor of the battery housing.

[0022] A battery cooling system includes a battery enclosure and N battery cells disposed within the battery enclosure and having a rigid outer surface, where N is an integer greater than one. A wicking material is disposed 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.

[0023] Other features include a separator in fluid communication between the condenser and the pump. A heat exchanger is located above the vapor distributor of the battery housing.

[0024] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are for illustrative purposes only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 shows a functional block diagram of an exemplary battery cooling system having a battery casing and wick assemblies disposed between adjacent battery cells in accordance with the present disclosure; Fig. 2 shows an exemplary battery case, exemplary battery cells, and wick assemblies according to the present disclosure in a side cross-sectional view; Fig. 3 shows exemplary wick assemblies with a wick structure disposed between the end plates in accordance with the present disclosure, in an exploded view; Fig. 4 shows an exemplary wick material forming part of the wick structure according to the present disclosure; and Fig. 5 shows a battery housing with battery cells with rigid side surfaces and a wicking material arranged around the rigid side surfaces of the battery cells, in a perspective view.

[0026] Reference symbols may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0027] A battery cooling system according to the present disclosure utilizes the evaporation of dielectric fluid to cool a battery system. While the above disclosure is described in the context of a battery electric vehicle (BEV) or a hybrid vehicle, the battery cooling system may also be used to cool battery systems in other applications.

[0028] The battery cooling system cools by evaporating a small amount of dielectric fluid that is applied to the surfaces of the battery cells. In other words, a smaller amount of dielectric fluid is used rather than substantially filling a battery case with dielectric fluid. In some examples, the battery case needs to be filled with dielectric fluid to less than 20% (and in some cases, less than 10%) of the height of the battery case, although larger or smaller amounts of dielectric fluid may be used.

[0029] In various examples described below, a wicking material is used to draw dielectric fluid located in a lower portion of the battery case upward by capillary action, enabling heat exchange with the sides of the battery cells. The dielectric fluid absorbs heat from the sides of the battery cells, resulting in vaporization of the dielectric fluid. The vapor rises, is collected in a vapor distributor, condensed, and pumped back into the battery case.

[0030] The cooling effect of 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 the energy consumption for the pumping process and the required pumping power.

[0031] With reference now to Fig. 1, a battery cooling system 10 is shown including a battery housing 20 within which a plurality of battery cells 24 are disposed. In some examples, the battery cells 24 comprise pouch battery cells that are generally rectangular and arranged in a horizontal longitudinal direction. The pouch battery cells have a non-rigid outer surface and are generally compressed within the battery housing. In other examples, the battery cells comprise other shapes, such as cylindrical, prismatic, or other shapes.

[0032] In Fig. 1 is a cross-sectional view of a wick material of a wick assembly 40 disposed between two battery cells 24 to show the pumping of the dielectric fluid along the outer surfaces of the battery cells due to capillary action and evaporation of the dielectric fluid into vapor channels.

[0033] A vapor distributor 22 is disposed over the plurality of battery cells 24 to collect the vapor escaping from the vapor channels. The wick assembly 40 includes a wick material 44 that wicks the dielectric liquid 60 into Fig. 1 upward along the outer surfaces of the battery cells 24. In some examples, the wick material includes a wire mesh or a porous structure. In some examples, the wick material is made of copper, aluminum, nickel, ceramic, stainless steel, or another suitable material.

[0034] As the dielectric fluid moves upward through the capillary action of the wick material 44 (as shown by arrows 48), the heat from the battery cells 24 is absorbed by the dielectric fluid 60, resulting in vaporization. The vapor moves through the vapor channels 54 disposed between the wick material 44 (as shown by arrows 58) into the vapor manifold 22.

[0035] The vaporized dielectric fluid (arrows 58) flows upward into the vapor manifold 22. In some examples, a heat exchanger 70 may be disposed above the vapor manifold 22 to provide additional cooling or in-situ condensation. In some examples, the heat exchanger 70 is an air- or liquid-based heat exchanger.

[0036] 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 create 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 may be used to separate water or other contaminants from the dielectric fluid.

[0037] An outlet of the separator 80 is connected via a line 82 to an inlet of a pump 84. In some examples, Δp c + Δp pump > Δp v + Δp l + p l gh, where Δp c the pressure change due to capillary action, Δp pump the pressure change of the pump, Δp v the vapor pressure, Δp l the liquid pressure, g the gravity and h the height of the battery case.

[0038] An outlet of pump 84 delivers the dielectric fluid via a conduit 86 to an inlet located at a lower portion of battery case 20. The placement and geometry of the wicks and vapor channels are tailored to the heat distribution of a particular battery cell to ensure 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 may be used.

[0039] With reference now to Fig. 2 shows a cross-sectional view of the battery case 20. The battery case 20 houses a plurality of battery cells 24-1, 24-2, ..., 24-N arranged side by side. The wick assemblies 40-1, 40-2, ..., 40-M are arranged between adjacent pairs of battery cells 24-1, 24-2, ..., 24-N. In some examples, the wick assemblies 40-1, 40-2, ..., 40-M have a side cross-section approximately the same as that of the plurality of battery cells 24-1, 24-2, ..., 24-N.

[0040] With reference now to Fig. 3, the wick assembly 40 includes a first end plate 110 and a second end plate 112, between which a wick structure 114 is disposed. The first and second end plates 110 and 112 and the wick structure 114 are designed to operate with the horizontal compression used for pouch battery cells.

[0041] In some examples, the first end plate 110 and the second end plate 112 include vertical plate portions 120 that are spaced apart from each other in the horizontal direction. The horizontal plate portions 122 extend between the vertical plate portions 120 and are also spaced apart from each other in the vertical direction. Openings 124 are defined between the vertical plate portions 120 and the horizontal plate portions 122 of the first end plate 110 and the second end plate 112.

[0042] The wick structure 114 is comprised 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 comprised of copper, aluminum, nickel, ceramic, stainless steel, or other suitable wicking material. The wicking structure 114 includes outer surfaces defining protrusions 134. The protrusions 134 extend outwardly and are received by the openings 124 in the first end plate 110 and the second end plate 112 when the wicking unit 40 is assembled. In some examples, the openings 124 and the protrusions 134 are generally rectangular, although other shapes may be used.

[0043] The wick structure 114 also defines vapor escape channels 142 that extend vertically at spaced horizontal locations. In some examples, P of the protrusions 134 are aligned with the positions 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) protrusions on each side of the wick structure 114. The nested arrangement of the protrusions 134 and the openings 124 in the first and second end plates 110 and 112 prevents the vapor escape channels 142 from collapsing upon compression between the pouch battery cells.

[0044] With reference now to Fig. 3 and Fig. 4 shows another example of a wick material. In some examples, the wick structure 114 is made of a wire mesh, although other types of wick materials may be used. Fig. 4, the wire mesh comprises wires 90 woven into a wire mesh. In some examples, the wick structure 114 includes a first portion 150 and a second portion 152 that have the same shape. In some examples, the first portion 150 and the second portion 152 of the wick structure are stamped into the wire mesh, although other methods may be used.

[0045] The first portion 150 is mirrored relative to the second portion 152 and is attached to the second part 152 by the outwardly directed projections 134. In some examples, the first and second end plates 110 and 112 are made of a relatively rigid material. For example, the first and second end plates 110 and 112 may be made of a material selected from a group consisting of mica, garolite, and aerogel, although other materials may also be used.

[0046] With reference now to Fig. 5 shows another battery cooling system 200 that includes a battery housing 210 with a plurality of battery cells 220. The battery cells may include various battery cell formats, such as pouch, cylindrical, prismatic, or other formats. In some examples, the battery cells have rigid outer surfaces (compared to pouch cells). For example, the plurality of battery cells 220 may have cylindrical or rectangular outer surfaces, although other shapes may be used. The plurality of battery cells 220 are arranged side by side within the battery housing 210. A wicking material 224 is arranged around the 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.

[0047] In some examples, the wick material is made of copper, aluminum, nickel, ceramic, stainless steel, or another suitable material.

[0048] The dielectric fluid 226 is located in a lower portion of the battery case 210. The wicking material 224, disposed on the outer surfaces of the plurality of battery cells 220, draws the dielectric fluid 226 upward 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. The vapor is collected in a vapor distributor 234, condensed, and returned to the battery case 210 as described above. In some examples, the battery cooling system 200 is configured as shown in Fig. 1. connected as shown.

[0049] The battery cooling system according to the present disclosure provides evaporative cooling with dielectric fluid on the surfaces of the battery cells. The battery cooling system uses evaporative cooling in combination with dielectric fluid and external circuits for battery cooling. The wick assembly includes wick structures, such as thin screens, to move dielectric coolant upward along the outer surfaces of the battery cells. The wick assembly includes wick structures, such as thin screens, with additional pump assistance to move the dielectric coolant in the cooling circuit. The shape, size, and position of the wicks are tailored to address uneven heat distribution within a battery cell and improve temperature uniformity. The wick assemblies provide combined cooling and compression functions for pouch battery cells.

Claims

[1] Wick arrangement (40) for battery cells (24, 220) of a battery cooling system (10, 200), comprising: a first end plate (110) having vertical plate sections (120) and horizontal plate sections (122) defining openings (124); a second end plate (112) having vertical plate portions (120) and horizontal plate portions (122) defining openings (124); and a wick structure (114) made of a wick material (224) defining projections (134) on its first and second outer surfaces and containing a plurality of vapor outlet channels (142), wherein the wick structure (114) is adapted to be disposed between the first end plate (110) and the second end plate (112). [2] The wick assembly (40) of claim 1, wherein the projections (134) on the first and second outer surfaces of the wick structure (114) are received in the openings (124) of the first or second end plate (110, 112). [3] The wick assembly (40) of claim 1, wherein the projections (134) on the first outer surface and the second outer surface are aligned vertically with the plurality of vapor exit channels (142). [4] The wick assembly (40) of claim 1, wherein the plurality of vapor exit channels (142) extend in a vertical direction of the wick structure (114). [5] The wick assembly (40) of claim 1, wherein the wick structure (114) is selected from a group consisting of wire mesh and a porous material. [6] The wick assembly (40) of claim 1, wherein the first and second end plates (110, 112) are made of a material selected from a group consisting of mica, garolite, and aerogel. [7] Battery cooling system (10, 200), comprising: a battery case (20, 210); M wick assemblies (40) according to claim 1, wherein M is an integer greater than one; and N battery cells (24, 220), where N is an integer greater than one, wherein each of the M wick assemblies (40) is arranged between adjacent N battery cells (24, 220). [8] Battery cooling system (10, 200) according to claim 7, further comprising: a vapor distributor (22, 234) defined by the battery housing (20, 210) above the N battery cells (24, 220); a condenser (76) in fluid communication with the vapor distributor (22, 234); and a pump (84) having an inlet in fluid communication with the condenser (76) and an outlet in fluid communication with an inlet of the battery housing (20, 210). [9] Battery cooling system (10, 200) according to claim 8, further comprising a separator (80) arranged in fluid communication between the condenser (76) and the pump (84). [10] Battery cooling system (10, 200) according to claim 8, further comprising a heat exchanger (70) arranged above the vapor distributor (22, 234) of the battery housing (20, 210).

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