Battery pack with phase change material (PCM) composite

Abstract

To provide a solution for improving battery thermal management (BTM) and flame retardancy in a battery pack.SOLUTION: The battery pack includes a plurality of battery cells and a thermally conductive layer disposed between two battery cells of the plurality of battery cells and configured to transfer heat away from each of the two battery cells. The thermally conductive layer includes expanded graphite (EG) impregnated with a phase change material (PCM). The PCM may comprise organic and / or inorganic PCM materials. A thin thermal insulation barrier such as aerogel may be sandwiched between two anisotropic EG / PCM composites to regulate the temperature and prevent thermal runaway.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This U.S. non-provisional patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 675,283, filed July 25, 2024, the contents of which are incorporated herein by reference in their entirety. The present disclosure relates generally to phase change materials (PCMs) for battery thermal management (BTM) and flame retardancy. [Background technology]

[0002] Thermal management is an important consideration for battery packs, such as those used in electric vehicles (EVs). Flame retardancy, including preventing and mitigating the effects of battery fires, is also important, especially for batteries with high energy concentrations and / or that may contain volatile compounds. Summary of the Invention

[0003] The present disclosure provides a battery pack including a plurality of battery cells and a thermally conductive layer disposed between two battery cells of the plurality of battery cells and configured to transfer heat from each of the two battery cells, wherein the thermally conductive layer includes expanded graphite (EG) impregnated with a phase change material (PCM). These and other aspects of the present disclosure are set forth in the following detailed description, the appended claims, and the accompanying drawings. Further details, features, and advantages of the inventive design will be apparent from the following description of exemplary embodiments with reference to the associated drawings. [Brief explanation of the drawings]

[0004] [Figure 1A] FIG. 1 is a cutaway side view of a first battery pack having a conventional PCM thermally conductive layer. [Figure 1B] FIG. 1 is a cutaway top view of a first battery pack having a conventional PCM thermally conductive layer. [Figure 2A]FIG. 10 is a cutaway side view of a second battery pack according to the present disclosure. [Figure 2B] FIG. 10 is a cutaway top view of a second battery pack according to the present disclosure. [Figure 3A] FIG. 10 is a cutaway side view of a third battery pack according to the present disclosure. [Figure 3B] FIG. 10 is a cutaway top view of a third battery pack according to the present disclosure. [Figure 4] FIG. 10 shows a fourth battery pack with nine prismatic LMO battery cells, each separated by a copper foam and paraffin composite PCM thermally conductive layer. [Figure 5] FIG. 10 shows a fifth battery pack with nine prismatic LMO battery cells, each separated by a thermally conductive layer of pure paraffin PCM. [Figure 6] 10 is a graph showing temperature as a function of time for the fourth and fifth battery packs and another battery pack with natural convection cooling. [Figure 7A-7C] 10A-10C illustrate various assembly steps of a sixth battery pack according to the present disclosure. [Figure 8] 1 is a graph of temperature over time for a battery module with natural air convection (NAC) cooling. [Figure 9] 1 is a graph of temperature over time for a battery module with a hard block LDPE material cooling jacket. [Figure 10] 10 is a graph of temperature over time for a battery module with a flexible composite phase change material cooling jacket. DETAILED DESCRIPTION OF THE INVENTION

[0005] The present invention will now be described in detail in terms of the following embodiments with reference to the drawings. The present disclosure provides a solution to improve battery thermal management (BTM) and flame retardancy in battery packs by incorporating expanded graphite (EG) and thermal barrier layers into flexible phase change material (PCM) composites, a radical departure from conventional rigid pure PCM solutions. In some embodiments, conductive expanded graphite (EG) fillers are used to enhance the inherently low thermal conductivity of pure PCMs. This improves heat dissipation to the heat sink, thereby regulating the peak temperature of the battery cell below safe limits. Styrene butadiene rubber (SBR) can be used as a binder for EG particles in EG / paraffin PCM composites. SBR can help maintain the structural integrity and heat transfer properties of the material over thousands of PCM melting / solidification cycles. EG has a capillary microstructure, which can help prevent leakage when the PCM is in a molten (liquid) state. Using EG and SBR in a 1:1 mass ratio with DI water as the diluent results in a conductive porous EG foam with non-blocking micropores that can act as a host for the PCM material.

[0006] In some embodiments, the EG / PCM composite may include an anisotropic intervening layer, which can be configured to balance enhanced heat dissipation to the heat sink with improved thermal insulation between adjacent cells. In some embodiments, a composite sheet of EG / PCM can be compressed using a pneumatic vice to align the graphene sheets perpendicular to the direction of the compressive force, resulting in high in-plane thermal conductivity k in the direction coincident with the plane of the graphene sheets. 面内 Advantageously, the compressed composite sheet can also produce low out-of-plane thermal conductivity k in the direction perpendicular to the plane of the aligned graphene sheets. 面外 This compression can result in thermal energy following the path of least resistance and being transferred primarily to the heat sink below the composite sheet. This compression can be particularly advantageous for large battery packs that have a cold plate attached to the bottom of the cover for liquid cooling. This compression may not be as valuable for small replaceable packs that are subjected to forced air cooling (FAC) on all sides of the cover.

[0007] In some embodiments, a thin insulating barrier (such as aerogel) may be sandwiched between two anisotropic EG / PCM composites to regulate temperature and prevent thermal runaway in the event of an accident that could damage the battery pack, for example. The ultralow thermal conductivity of the insulating barrier (e.g., approximately 0.03 W / mK) can help prevent a combustion flame from spreading from a damaged battery cell to adjacent cells. In the event of a real fire, the intumescent flame-retardant (IFR) properties of EG can be utilized to suppress the combustion flame. Extreme heat breaks down the weak van der Waals forces between the graphene sheets (which make up the EG particles), causing the graphene layers in the EG to expand. This expansion of the EG creates a protective insulating cover for the flammable PCM.

[0008] In some embodiments, the BTM module may include trace amounts of one or more polymers, such as low-density polyethylene (LDPE), as additives to impart flexibility to the PCM composite structure. Such added polymers can improve the shock / impact absorption of the cells over rough and uneven terrain. For battery packs with cylindrical cells, flexible PCM composites can improve overall energy density and facilitate better integration with the pack's air-cooling system. For some applications, such as motorcycles with small (replaceable) battery packs subjected to simple forced air cooling (FAC) on two or more surfaces, the thermal barrier may only comprise EG and a thin thermal barrier (such as aerogel). The added cost and complexity of making the EG / PCM composite anisotropic may not be justified. Directional heat transfer may not make much difference, especially if heat can be removed from two or more surfaces of the battery pack. For other applications, such as four-wheeled vehicles with large battery packs that use liquid cooling via attached cold plates and where directional heat transfer plays a key role, it may be advantageous for the thermal barrier to include an anisotropic EG and a thin thermal barrier. In some embodiments, the BTM module may include an inorganic PCM as an alternative to paraffin-based organic PCM materials. Such inorganic PCM materials can further enhance safety by completely preventing combustion flames under accidental thermal events. Salt hydrates are inexpensive and have a high enthalpy of fusion (ΔH 融解 ) and is essentially non-flammable due to its high water content.

[0009] 1A-1B show cutaway side and top views of a first battery pack 10 having two battery cells 12 and a conventional PCM thermally conductive layer 30 disposed therebetween. Each battery cell 12 includes two electrical terminals 14 on its top surface. A heat sink 20 is disposed adjacent to the lower edge of the battery cell 12 opposite the electrical terminals. The heat sink 20 includes a plate 22 of a thermally conductive material, such as metal. The heat sink 20 also includes a plurality of fins 24 that protrude below the plate 22 on the side opposite the battery cells 12 and conduct heat away from the battery cells 12. The PCM thermally conductive layer 30 is sometimes referred to as an intervening layer because it is disposed in the space between the battery cells 12. The PCM thermally conductive layer 30 may include only a PCM material, such as paraffin. The PCM thermally conductive layer 30 of the first battery pack 10 provides relatively low thermal conductivity, which results in poor heat dissipation to the heat sink 20 and may cause the temperature of the battery cells 12 to become undesirably high.

[0010] 2A-2B show cutaway side and top views of a second battery pack 110 of the present disclosure. The second battery pack 110 may be similar to or identical to the first battery pack 10, except for certain differences described herein. The second battery pack 110 includes a first composite thermally conductive layer 120 in place of the conventional PCM thermally conductive layer 30. The first composite thermally conductive layer 120 includes expanded graphite (EG) impregnated with a PCM material. The PCM material may include an organic PCM, such as a paraffin-based material. Additionally or alternatively, the PCM material may include one or more inorganic PCM materials, such as salt hydrates. The first composite thermally conductive layer 120 may be referred to as an EG / PCM composite. The first composite thermally conductive layer 120 provides relatively high thermal conductivity, which may enhance heat dissipation to the heat sink 20. This thermal conductivity also facilitates heat exchange between adjacent battery cells 12 if one of the battery cells 12 overheats, which can propagate overheating between the battery cells 12 and cause undesirable cascading events.

[0011] 3A-3B show cutaway side and top views of a third battery pack 210 of the present disclosure. The third battery pack 210 may be similar to or identical to the second battery pack 110, except for certain differences described herein. The third battery pack 210 includes a hybrid thermally conductive layer 220, 222, which includes two aligned EG layers 220 separated by a thermal barrier 222. The aligned EG layer 220 may include EG material compressed by a vice to align graphene sheets therein. The aligned EG layer 220 may be anisotropic, such that its thermal conductivity is significantly higher in a first direction than in a second direction perpendicular to the first direction. The first direction may correspond to aligned graphene sheets. The aligned EG layers 220 may each be impregnated with a PCM material, such as an organic and / or inorganic PCM material. The thermal barrier 222 may be a relatively thin layer of a material with a relatively low ability to transfer heat, such as aerogel. Therefore, the third battery pack 210 can enhance heat dissipation to the heat sink 20 and simultaneously retard excessive heat exchange between adjacent battery cells 12. The vice compression aligns the graphene sheets, allowing heat to be conducted primarily toward the heat sink 20. A thin layer of thermal barrier 222 is sandwiched between the two EG / PCM composites 220.

[0012] 4 shows a fourth battery pack 310. The fourth battery pack 310 includes a case 312 that provides a liquid-tight seal. The case 312 may be made of a polymer such as acrylic. In some embodiments, one or more portions of the case 312 may be made of a thermally conductive material such as metal. The case 312 of the fourth battery pack 310 houses nine prismatic lithium-ion manganese oxide (LMO) battery cells 12, each separated by a thermally conductive layer 320 that includes a copper (Cu) foam and paraffin composite PCM. 5 shows a fifth battery pack 350. The fifth battery pack 350 may be similar to or identical to the fourth battery pack 310, except for the differences described herein. The fifth battery pack 350 includes a case 312 containing nine prismatic LMO battery cells 12, each separated by a thermally conductive layer 360 of pure paraffin PCM. FIG. 6 shows a graph illustrating temperature as a function of time for the fourth and fifth battery packs and another battery pack with natural convection cooling.

[0013] 7A-7C show various assembly steps for a sixth battery pack 410. The sixth battery pack 410 includes a case 312 that houses four cylindrical battery cells 412. The sixth battery pack 410 further includes a thermal barrier 414 disposed between the four cylindrical battery cells 412. The thermal barrier 414 may include aerogel felt. A PCM filler 416, such as EG infiltrated with a PCM material, such as an organic and / or inorganic PCM material, fills the space around the four cylindrical battery cells 412 and aids in heat transfer from each of the four cylindrical battery cells 412 to the case 312. The present disclosure provides a battery pack including an EG / PCM / aerogel thermally conductive layer that can significantly reduce the likelihood of fire ignition and / or the severity of a fire resulting from a thermal runaway condition.

[0014] Figure 8 shows a graph of temperature over time for a battery module with natural air convection (NAC) cooling, Figure 9 shows a graph of temperature over time for a battery module with a rigid block LDPE material cooling jacket, and Figure 10 shows a graph of temperature over time for a battery module with a flexible composite phase change material cooling jacket. The foregoing description is not intended to be exhaustive or to limit the present disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment and, where applicable, may be interchangeable and used in selected embodiments even if not specifically shown or described. The foregoing may be varied in many ways. Such variations are not to be considered departures from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure. [Explanation of symbols]

[0015] 10 First Battery Pack 12 battery cells 14 Electrical terminals 20 Heat sink 22 Plate 24 Finn 30 PCM thermal conductive layer 110 Second Battery Pack 120 First composite thermally conductive layer 210 Third Battery Pack 220 Hybrid thermal conductive layer, aligned EG layer, EG / PCM composite 222 Hybrid heat conducting layer, thermal barrier 310 4th Battery Pack 312 cases 320 Thermal Conduction Layer 350 5th Battery Pack 360 Thermal Conduction Layer 410 6th Battery Pack 412 Cylindrical Battery Cell 414 Thermal Barrier 416 PCM filler

Claims

1. a plurality of battery cells; a thermally conductive layer disposed between two battery cells of the plurality of battery cells and configured to transfer heat from each of the two battery cells, the thermally conductive layer including expanded graphite (EG) impregnated with a phase change material (PCM); Including the battery pack.

2. 10. The battery pack according to claim 1, wherein the thermally conductive layer further comprises a binder of styrene butadiene rubber (SBR).

3. 3. The battery pack according to claim 2, wherein the thermally conductive layer comprises the EG and the SBR in a mass ratio of 1:

1.

4. 3. The battery pack of claim 2, wherein the thermally conductive layer comprises deionized (DI) water for diluting the SBR.

5. 10. The battery pack of claim 1, wherein the expanded graphite is anisotropic defining a relatively high in-plane thermal conductivity in a first direction and a relatively low out-of-plane thermal conductivity in a second direction perpendicular to the first direction.

6. 10. The battery pack of claim 1, wherein the thermally conductive layer further comprises a thermal insulating barrier sandwiched between two layers of the EG impregnated with the PCM.

7. 7. The battery pack of claim 6, wherein the thermal insulating barrier comprises an aerogel.

8. 7. The battery pack of claim 6, wherein the insulating barrier has a thermal conductivity of about 0.03 W / m-K or less.

9. 10. The battery pack of claim 1, wherein the thermally conductive layer further comprises a polymer additive to enhance flexibility.

10. 10. The battery pack of claim 9, wherein the polymer additive comprises low density polyethylene (LDPE).

11. 10. The battery pack of claim 1, wherein the PCM comprises a paraffin-based material.

12. The battery pack of claim 1 , wherein the PCM comprises an inorganic PCM material.

13. The battery pack of claim 12 , wherein the inorganic PCM material comprises a salt hydrate.

14. 2. The battery pack according to claim 1, wherein each battery cell of the plurality of battery cells has a cylindrical shape, and the thermally conductive layer is configured as a jacket annularly covering each battery cell of the plurality of battery cells.

15. 15. The battery pack according to claim 14, wherein the jacket of the thermally conductive layer is flexible to conform to the cylindrical shape of a corresponding battery cell of the plurality of battery cells.

16. 15. The battery pack of claim 14, wherein the jacket of the thermally conductive layer is formed rigidly.

17. 10. The battery pack of claim 1, further comprising a case enclosing the plurality of battery cells, the battery pack being configured to transfer heat to the case and dissipate it therefrom by forced air cooling (FAC).

18. 2. The battery pack of claim 1, wherein each battery cell of the plurality of battery cells has one of a prismatic shape or a pouch shape, and the thermally conductive layer is configured as a flat plate disposed between each adjacent battery cell of the plurality of battery cells.

19. 20. The battery pack of claim 18, further comprising a heat sink extending perpendicular to the thermally conductive layer and configured to dissipate heat therefrom.

20. 20. The battery pack of claim 19, wherein the heat sink is configured to conduct a liquid therethrough to remove the heat from the heat sink.

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