WO2016166659A1

WO2016166659A1 - Battery module

Info

Publication number: WO2016166659A1
Application number: PCT/IB2016/052071
Authority: WO
Inventors: Robert Ball; John Lewis
Original assignee: Tata Motors European Technical Centre Plc; Tata Motors Limited
Priority date: 2015-04-13
Filing date: 2016-04-12
Publication date: 2016-10-20
Also published as: GB2537431B; GB201511127D0; GB2537431A

Abstract

The present disclosure relates to a battery module for a traction battery. The battery module comprises a plurality of battery cells and a plurality of heat transfer members. A cooling plate is provided to transfer heat from the heat transfer members. An electrical grounding connector is electrically connected to each said heat transfer member. The electrical grounding connector comprises an electrically conductive elastomer. The present disclosure also relates to a traction battery; and to a vehicle.

Description

BATTERY MODULE

TECHNICAL FIELD

The present disclosure relates to a battery module, to a traction battery, and to a vehicle comprising a battery module.

BACKGROUND

Large battery packs such as used in electric vehicle traction applications are typically made up of a number of battery modules. Each module consists of a plurality of battery cells connected in such a way as to provide the module voltage and capacity required. Modules are then connected together to form a high voltage (HV) battery pack providing overall pack voltage and energy requirements. Electrical isolation is required between each cell and the heat transfer plate within a battery module to prevent a short circuit from the battery HV to vehicle ground in the event of a cell malfunction.

One approach is to coat the heat transfer plates with an electrically insulating material which has minimal effect on heat flow between cell and the plate. This construction does not readily allow electrical grounding of the battery cells and/or the heat transfer plates. Electrical grounding can enable detection of a loss of electrical grounding of one or more battery module; and can reduce re-radiation of electromagnetic radiation by the heat transfer plates.

It is against this backdrop that the present invention has been conceived. At least in certain embodiments, the present invention provides an improved battery module.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a battery module; to a traction battery; and to a vehicle. According to a further aspect of the present invention there is provided a battery module for a traction battery, the battery module comprising:

a plurality of battery cells;

a plurality of heat transfer members;

a cooling plate for transferring heat from the heat transfer members; and an electrical grounding connector electrically connected to each said heat transfer member; wherein the electrical grounding connector comprises an electrically conductive elastomer. Optionally, the electrically conductive elastomer is resilient and is typically compressed against the heat transfer members to form the electrical connection. This arrangement helps to accommodate variations in the alignment of the heat transfer members. Moreover, at least in certain embodiments, the resulting electrical connection is vibration resistant, helping to absorb operational vibrations.

The battery cells are typically arranged in an array within the battery module. At least one heat transfer member is associated with each battery cell. One of said heat transfer members can be disposed between adjacent battery cells in the battery module. In certain embodiments the battery cells each have first and second major surfaces. At least one of the first and second major surfaces can be disposed in a face-to-face arrangement with one of said heat transfer members. The electrical grounding connector may be deformable to conform to irregularities in the alignment of the heat transfer members relative to each other and/or other components in the traction battery. In certain embodiments, the heat transfer members are not fixedly mounted within the battery module. This resulting floating arrangement of the heat transfer members can result in variations in their relative alignment.

The electrical grounding connector can comprise a silicone elastomer or a fluorosilicone- elastomer loaded with electrically conductive particles. The electrically conductive particles can comprise one or more of the following set: nickel particles, nickel plated graphite particles, silver plated aluminium particles, and silver plated copper particles.

Each heat transfer member can comprise an electrically conductive substrate and an electrically insulating coating. The electrically conductive substrate can be formed from metal. For example, the electrically conductive substrate can be formed from sheet metal. The electrically conductive substrate can be made of aluminium, but other materials are also contemplated. The electrically insulating coating is applied to the exterior of the electrically conductive substrate.

One or more coating aperture can be formed in said electrically insulating coating to establish an electrical connection between said electrically conductive substrate and the electrical grounding connector. The heat transfer member may comprise at least one contact surface, and at least one flange. The one or more coating aperture could be formed in the at least one contact surface or at an edge thereof. Alternatively, the one or more coating aperture can be formed in the electrically insulating coating on said at least one flange. In use, each contact surface is disposed in contact with an adjacent battery cell. In use, the at least one flange can be disposed alongside one or more of said battery cells. The flange can, for example, be positioned alongside an edge, a side wall or an end wall of one or more of said battery cells. The flanges of the heat transfer members can be arranged alongside each other. The electrical grounding connector can comprise an elongate strip extending transversely across the flanges of said plurality of heat transfer members.

The electrical grounding connector can be compressed against said heat transfer members so as at least substantially to conform to the shape of the heat transfer members. This can help to establish electrical contact with said heat transfer members.

The electrical grounding connector can be adhesively attached to each heat transfer member.

The electrical grounding connector can be disposed between said heat transfer members and the cooling plate. The electrical grounding connector can be compressed between said heat transfer members and the cooling plate so as at least substantially to conform to the shape of the heat transfer members and/or the cooling plate. For example, the electrical grounding connector can be compressed when the cooling plate is mounted during assembly of the battery module. This can establish and maintain the electrical contact between the heat transfer members and the cooling plate.

A thermally conductive interface can be disposed between said heat transfer members and the cooling plate. The thermally conductive interface can comprise a deformable material. The thermally conductive interface can be deformed so as at least substantially to comply with the shape of the heat transfer members and/or the cooling plate. The mounting of the cooling plate during assembly of the battery module can cause the thermally conductive interface to deform.

The thermally conductive interface can be electrically insulating.

The thermally conductive interface can be disposed adjacent to the electrically conductive elastomer. The thermally conductive interface and the electrically conductive elastomer can be arranged in a non-overlapping arrangement. A channel or cut-out can be formed in the thermally conductive interface to accommodate the electrically conductive elastomer. Alternatively, the electrically conductive elastomer can be disposed along an edge of the thermally conductive interface. The electrically conductive elastomer can be in the form of an elongate strip.

At least in certain embodiments, the thermally conductive interface and the electrical grounding connector can conform to the shape of the heat transfer members and/or the cooling plate. The thermally conductive interface and the electrically conductive elastomer can establish electrical and thermal connections between the heat transfer members and the cooling plate. Thus, the thermally conductive interface and the electrically conductive elastomer form a composite layer to provide thermal and electrical connections between the heat transfer members and the cooling plate.

The cooling plate can be a heat sink. In certain embodiments, the cooling plate can be actively cooled. For example, in use, the cooling plate can be cooled by a coolant liquid. The coolant liquid can be circulated through a chamber formed in the cooling plate.

According to a further aspect of the present invention there is provided a traction battery comprising a plurality of the battery modules described herein.

According to a still further aspect of the present invention there is provided a vehicle comprising a traction battery as described herein.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a schematic representation of a vehicle incorporating a traction battery in accordance with an embodiment of the present invention; Figure 2 shows a perspective view of a battery module forming the traction battery shown in Figure 1 ;

Figure 3 shows a vertical cross section through the battery module shown in Figure

2;

Figure 4 shows a horizontal cross section of the battery module shown in Figure 2; and

Figure 5 shows an exploded perspective view of a heat transfer member and associated first and second battery cells in the battery module shown in Figure 2. DETAILED DESCRIPTION

A traction battery 1 comprising a plurality of battery modules 2 in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures. The traction battery 1 is configured to supply electrical energy to one or more electric machine 3 to propel a vehicle 4, as shown schematically in Figure 1 . The vehicle 4 in the present embodiment is an automobile, but the invention is not limited in this respect.

The present invention will now be described with reference to one of the battery modules 2. The traction battery 1 comprises a plurality of like battery modules 2 (labelled 2-1 , 2-2... 2-n in Figure 1 ). A perspective view of one of the battery modules 2 is shown in Figure 2. A vertical sectional view of the battery module 2 is shown in Figure 3; and a horizontal sectional view of the battery module 2 is shown in Figure 4. The battery module 2 comprises a plurality of battery cells 5 and an electronic control unit (ECU). In the present embodiment, the battery cells 5 are lithium ion cells but other cell compositions are also contemplated. The battery cells 5 can have various configurations, including cylindrical, rectangular (prismatic) and pouch cells. In the present embodiment the battery cells 5 are pouch cells each having a pouch formed from a flexible material. As shown in Figure 5, the battery cells 5 comprise first and second major surfaces 6-1 , 6-2; upper and lower end walls 7-1 , 7-2; and first and second side walls 8-1 , 8-2. In the case of a pouch cell, the end walls 7-1 , 7-2 and/or the side walls 8-1 , 8-2 can be in the form of edges formed by folding or joining the flexible material to form the pouch. The battery cells 5 are mounted in a housing 9 in a uniform array. The battery cells 5 are disposed in the housing 9 such that the first and second major surfaces 6-1 , 6-2 of adjacent battery cells 5 are arranged in a face-to-face arrangement. This configuration allows more battery cells 5 to be accommodated within a given volume and can thus provide a greater energy density. The first and second major surfaces 6-1 , 6-2 of the battery cells 5 have a large surface area to facilitate cooling. In the present embodiment the first and second major surfaces 6-1 , 6-2 are generally rectangular. In normal operation the battery cells 5 generate heat in proportion to the rate of charge/discharge. To provide cooling of the battery modules 2, heat transfer plates 10 are sandwiched between pairs of the battery cells 5. As shown in Figure 5, the heat transfer plates 10 each comprise first and second contact surfacesl 1 -1 , 1 1 -2, first and second lateral flanges 12-1 , 12-2 and a bottom flange 12-3. The first and second lateral flanges 12-1 , 12-2 and the bottom flange 12-3 are disposed substantially perpendicular to the first contact surface 1 1 -1 . The heat transfer plates 10 provide a thermally conductive path to transfer thermal energy from the battery cells 5 to a cooling plate 13 positioned along a lateral side of the housing 9. The cooling plate 13 is externally cooled by a liquid coolant pumped through a supply conduit 15. The first and second lateral flanges 12-1 , 12-2 are disposed laterally outside the first and second side walls 8-1 , 8-2 of the battery cells 5. The first lateral flange 12-1 is disposed adjacent to the cooling plate 13. The heat transfer plates 10 each comprise an electrically conductive substrate 16 having a coating 17. In the present embodiment, the electrically conductive substrate 16 is formed from aluminium, but other conductive materials are contemplated. The heat transfer plate coating 17 is electrically insulating and is applied to electrically isolate the battery cells 5. Electrical isolation is required between the battery cells 5 and the heat transfer plates 10 to prevent a short circuit from the battery HV to vehicle ground in the event of a malfunction of a battery cell 5. BS EN1987-1 :1997 Electrically Propelled Vehicle Safety Requirements specifies that high voltage (HV) to ground isolation should be 2x pack voltage + 1000V. For a typical 400V pack this equates to a 1.8kV isolation requirement. The heat transfer plate coating 17 is selected to provide electrical insulation with minimal effect on heat flow between the battery cell 5 and the electrically conductive substrate 16.

The first and second lateral flanges 12-1 , 12-2 and the bottom flange 12-3 are sized such that first and second battery cells 5-1 , 5-2 are received within each heat transfer plate 10. The first major surface 6-1 of the first battery cell 5-1 is disposed in face contact with the contact surface 1 1 of the associated heat transfer plate 10. The second major surface 6-2 of the second battery cell 5-2 is disposed in face contact with the contact surface 1 1 of an adjacent heat transfer plate 10. Thus, one of the first and second major surfaces 6-1 , 6-2 of each battery cell 5 is disposed in contact with one of said heat transfer plates 10. The heat transfer plates 10 are disposed within the housing 9 such that the first lateral flanges 12-1 are arranged in a substantially planar arrangement. It will be understood that due to manufacturing tolerances, the first lateral flanges 12-1 may be offset from each other. The cooling plate 13 is substantially planar and is disposed alongside the first lateral flanges 12-1 of each of the heat transfer plates 10. A thermally conductive interface 18 is disposed between the first lateral flanges 12-1 and the cooling plate 13 to establish a thermal conduction pathway between the first lateral flanges 12-1 and the cooling plate 13. The thermally conductive interface 18 is a compliant, malleable material formed into a continuous layer. When the battery module 2 is assembled, the thermally conductive interface 18 is deformed to fill any gaps or spaces between the heat transfer plates 10 and the cooling plate 13. The thermally conductive interface 18 can thereby reduce or eliminate air gaps and help to ensure that mechanical contact is established and maintained between the first lateral flanges 12-1 and the cooling plate 13. The transfer of heat from the heat transfer plates 10 to the cooling plate 13 is thereby performed efficiently. The thermally conductive interface 18 can be in the form of a compliant, thermally conductive 'gap pad' or 'gap filler' material available from Bergquist, Saint-Gobain, Kunze and others. These materials are thermally conductive but electrically insulating.

The battery modules 2 also comprise an electrical grounding connector 19 for establishing an electrical ground connection from each of the heat transfer plates 10 to a vehicle ground connection (not shown). In the present embodiment, the electrical grounding connector 19 is formed from an electrically conductive elastomeric material which is resiliently deformable. Suitable electrically conductive elastomeric materials are made from silicone or fluorosilicone elastomers loaded with conductive particles such as nickel, nickel plated graphite, silver plated aluminium or silver plated copper. These materials are available from commercial sources such as Kemtron and EuroTechnologies. The electrically conductive elastomeric materials typically have relatively poor thermal conductivity compared to the thermally conductive interface 18.

In the present embodiment the electrical grounding connector 19 is an elongate strip arranged to establish contact with each heat transfer plate 10 in the battery module 2. As shown in Figure 5, a coating aperture 20 is formed in the heat transfer plate coating 17 of each of the heat transfer plates 10 to expose the electrically conductive substrate 16. The coating apertures 20 are formed in like positions on each of the heat transfer plates 10 to facilitate alignment with the electrical grounding connector 19. In the present embodiment, the coating apertures 20 are formed in an outer surface 21 of the first lateral flanges 12-1 . The electrical grounding connector 19 is applied coincident with the coating apertures 20 to establish an electrical connection between the electrically conductive substrate 16 of each heat transfer plate 10 and the electrical grounding connector 19. An elongate channel or cutout (not shown) can be formed in the thermally conductive interface 18 to accommodate the electrical grounding connector 19. In the present embodiment, the electrical grounding connector 19 is disposed alongside the thermally conductive interface 18 in a non- overlapping configuration, as shown schematically in Figure 5. During assembly of the battery module 2, battery cells 5 and the heat transfer plates 10 are disposed in the housing 9. The thermally conductive interface 18 is applied to the first lateral flanges 12-1 of the heat transfer plates 10. The electrical grounding connector 19 is also applied to the first lateral flanges 12-1 and is positioned coincident with the coating apertures 20 formed in the heat transfer plate coating 17. The cooling plate 13 is mounted to the housing 9, thereby deforming the thermally conductive interface 18 and compressing the electrical grounding connector 19. The thermally conductive interface 18 and the electrical grounding connector 19 conform to the space between the heat transfer plates 10 and the cooling plate 13. The resulting composite layer, in use, provides thermal conductivity and establishes an electrical ground contact. The deformation of the thermally conductive interface 18 helps to ensure the efficient transfer of heat from the heat transfer plates 10 to the cooling plate 13. The compression of the electrical grounding connector 19 helps to ensure that a good electrical grounding connection is established between the heat transfer plates 10 and the cooling plate 13. The electrical connections established by the electrical grounding connector 19 are substantially immune to the effects of vibration, humidity and temperature change. The deformable nature of the thermally conductive interface 18 and the resilient nature of the electrical grounding connector 19 thereby complement each other. In the assembled battery module 2, the thermally conductive interface 18 and the electrical grounding connector 19 are disposed adjacent to each other in a non-overlapping arrangement. It will be appreciated that the thickness of the thermally conductive interface 18 and the electrical grounding connector 19 should be selected so as not to compromise either thermal or electrical performance.

The electrical grounding connector 19 is provided to provide a means of detecting loss of electrical isolation between the terminals of a battery cell 5 and the adjacent heat transfer plate 10. This could result for example, from an internal failure in the cell pouch structure, plus corrosive damage by the electrolyte or other released chemical to the heat transfer plate coating 17. Detection of such a loss of isolation is carried out by an isolation measurement circuit (not shown), which is a known technology and is fitted to HV batteries as a legal requirement. Failure to detect such fault could result in a short circuit from an HV node to a battery mechanical component which presents a potential risk for personnel servicing the vehicle. Furthermore, if the heat transfer plates 10 are not grounded, normal operation of the traction battery 1 could result in the heat transfer plates 10 acting as antennas and re-radiating electromagnetic energy generated by currents flowing through the battery. Such re-radiation induces unwanted electrical noise into signals of the battery management system which is highly undesirable. Otherwise, removing this noise by adding electrical filtering or screening components may add cost and/or weight to the traction battery 1 .

In a variant, the location of the coating apertures 20 and the corresponding positioning of the electrical grounding connector 19 can be modified. Rather than positioning the coating apertures 20 to establish a grounding connection with the cooling plate 13, they could be arranged to establish an electrical connection with the housing 9 or another support framework. For example, the coating 17 apertures 20 could be formed in the bottom flange 12-3 for establishing an electrical contact with the housing 9. It will be appreciated that various changes and modifications can be made to the battery module 2 described herein without departing from the scope of the present invention.

Claims

CLAIMS:

1 . A battery module for a traction battery, the battery module comprising:

a plurality of battery cells;

a plurality of heat transfer members;

a cooling plate for transferring heat from the heat transfer members; and an electrical grounding connector electrically connected to each said heat transfer member;

wherein the electrical grounding connector comprises an electrically conductive elastomer.

2. A battery module as claimed in claim 1 , wherein the electrical grounding connector is deformable to conform to irregularities in the arrangement of the heat transfer members.

3. A battery module as claimed in claim 1 or claim 2, wherein the electrical grounding connector comprises a silicone elastomer or a fluorosilicone-elastomer loaded with electrically conductive particles.

4. A battery module as claimed in claim 3, wherein said electrically conductive particles comprise one or more of the following set: nickel particles, nickel plated graphite particles, silver plated aluminium particles, and silver plated copper particles.

5. A battery module as claimed in any one of the preceding claims, wherein each heat transfer member comprises an electrically conductive substrate and an electrically insulating coating.

6. A battery module as claimed in claim 5, wherein one or more coating aperture is formed in said electrically insulating coating to establish an electrical connection between said electrically conductive substrate and the electrical grounding connector.

7. A battery module as claimed in claim 6, wherein each heat transfer member comprises at least one contact surface, and at least one flange; wherein said one or more coating aperture is formed in the electrically insulating coating on said at least one flange.

8. A battery module as claimed in claim 7, wherein the electrical grounding connector comprises an elongate strip extending transversely across the flanges of said plurality of heat transfer members.

9. A battery module as claimed in any one of the preceding claims, wherein the electrical grounding connector is adhesively attached to the heat transfer member.

10. A battery module as claimed in any one of the preceding claims, wherein the electrical grounding connector is compressed against said heat transfer members.

1 1 . A battery module as claimed in any one of the preceding claims, wherein the electrical grounding connector is disposed between said heat transfer members and the cooling plate.

12. A battery module as claimed in claim 1 1 , wherein the electrical grounding connector is compressed between said heat transfer members and the cooling plate.

13. A battery module as claimed in claim 1 1 or claim 12 comprising a thermally conductive interface disposed between said heat transfer members and the cooling plate.

14. A battery module as claimed in claim 13, wherein the thermally conductive interface is disposed adjacent to the electrically conductive elastomer.

15. A battery module as claimed in claim 13 or claim 14, wherein the thermally conductive interface comprises a deformable material.

16. A battery module as claimed in any one of claims 13, 14 or 15, wherein the thermally conductive interface and the electrical grounding connector conform to the shape of the heat transfer members.

17. A traction battery comprising a plurality of the battery modules claimed in any one of the preceding claims.

18. A vehicle comprising a traction battery as claimed in claim 17.

19. A battery module substantially as herein described with reference to the accompanying figures.

20. A vehicle substantially as herein described with reference to the accompanying figures.