WO2024013238A1

WO2024013238A1 - Top lid venting battery module

Info

Publication number: WO2024013238A1
Application number: PCT/EP2023/069335
Authority: WO
Inventors: Anneke Swierstra; Tomas VERHALLEN; Augustin ALMADA; Anne-Sophie Debruyne; Kilian MENZL
Original assignee: Northvolt Ab
Priority date: 2022-07-13
Filing date: 2023-07-12
Publication date: 2024-01-18
Also published as: SE2250902A1

Abstract

A battery module (100, 300,401, 402) comprising a plurality of secondary cells, each secondary cell of the plurality of secondary cells (110, 310, 410, 510) having a casing (111) and a failure vent (112, 312, 412, 413, 512, 513) in the casing for venting gases (480, 580) upon thermal failure of the secondary cell. The battery module further comprises a protective sheet (120, 220, 320, 420) extending above the plurality of secondary cells and arranged to cover the failure vents as well as a top cover configured to define a venting channel (470, 570) for guiding the vented gases away from the secondary cell. The protective sheet is configured to assume a first state (321, 421) in which it forms a barrier between the failure vent and the venting channel, and a second state (322, 422) in which it enables passage of the vented gases from the failure vent to the venting channel.

Description

TOP LID VENTING BATTERY MODULE

Technical field

The present disclosure generally relates to batteries for electric vehicles. More particularly, the present disclosure relates to venting of gases emitted by batteries for electric vehicles, especially in the case of thermal failure or thermal runaway.

Background

Rechargeable or secondary batteries find widespread use as electrical power supplies and energy storage systems. For example, in automobiles, battery packs formed of a plurality of battery modules, wherein each battery module includes a plurality of interconnected electrochemical cells, or secondary cells, are provided as a means of effective storage and utilization of electric power.

More particularly, there is a growing interest for optimizing the storage capacity of electric energy which is in part addressed by the plurality of interconnected secondary cells comprised in each battery module and/or by arranging a plurality of battery modules in a collection or pack. The arrangement of the connected cells will need to be protected from the environment, from moisture and vice versa from harmful exposure to high voltage equipment.

However, the increase in number of interconnected secondary cells forming part of a battery module also increases the risk of undesired events, such as the propagation of thermal failure from one to more secondary cells and in one or more battery module(s). During thermal failure, gases, and/or ejecta, are released from the one or more damaged secondary cells and travel quickly throughout the battery module, potentially triggering thermal failure of neighboring secondary cells and possibly of an entire battery module or stack of battery modules. Hence, there is a need for a solution preventing, or at least limiting, adverse effects related to events such as thermal failure from spreading amongst the secondary cells comprised in current battery modules.

Summary

Aspects and embodiments of the present disclosure relate to a battery module for electric vehicle having adaptations and improvements directed to solving one or more of the aforementioned problems.

These aspects and embodiments stem from the need of reducing the extent of the damage experienced by secondary cells of a battery module subsequently to thermal failure occurring in one or more of those secondary cells. It will be appreciated that “thermal failure” as used herein may be understood as thermal runaway and/or cell venting, thermal runaway representing the process by which the temperature in a secondary cell increases exponentially and cell venting representing the release of gases from the secondary cell. The aspects and embodiments of the present disclosure are further based on the idea of reducing the cost generated by battery modules experiencing thermal failure by attempting to increase the possible salvaging of secondary cells in damaged battery modules.

Hence, an object of the present disclosure lies in preventing, or at least limiting, gases and/or ejecta released from secondary cells incurring thermal failure to travel across neighboring healthy secondary cells and trigger thermal failure of these healthy secondary cells. A further object of the present disclosure lies in the at least partial isolation of the healthy secondary cells from the gases and/or ejecta released by the secondary cells incurring thermal failure and directing those gases and/or ejecta away from the healthy secondary cells. As used herein, “ejecta” may be understood as matter, liquid and/or solid, forced or thrown out of a secondary cell through the failure vent of that cell as a result of thermal failure occurring in that cell.

In particular, and according to a first aspect, there is provided a battery module, comprising a plurality of secondary cells, each secondary cell of the plurality of secondary cells having a casing and a failure vent in the casing for venting gases upon thermal failure of the secondary cell. It will be appreciated that the plurality of secondary cells may be arranged in an alignment such that at least one column of aligned secondary cells is formed between two end walls of a modular frame enclosing the plurality of secondary cells.

It will further be appreciated that a failure vent is configured to enable fluid communication between the casing of the secondary cell and its surroundings upon thermal failure of that secondary cell.

The battery module according to the first aspect further comprises a protective sheet extending above the plurality of secondary cells and arranged to cover the failure vents as well as a top cover configured to define a venting channel for guiding the vented gases away from the secondary cell. The protective sheet is configured to assume a first state in which it forms a barrier between the failure vent and the venting channel, and a second state in which it enables passage of the vented gases from the failure vent to the venting channel.

In the first state, the protective sheet may enable the sealing of each secondary cell and therefore the sealing of the failure vents of those secondary cells. This thereby permits at least partial isolation of each sealed secondary cell from one another. As used herein, “sealing” may be understood as at least partially sealed. That is, the protective sheet forming an at least partially fluid impermeable perimeter on a surface of each secondary cell it seals.

According to an embodiment of the present disclosure, the protective sheet may therefore be configured to form an at least partly sealed pocket above at least one of the failure vents. The pocket may be completely or substantially completely sealed by the protective sheet. The protective sheet thereby enables the formation of localized pockets wherein each pocket may be formed above, or cover, a secondary cell. It will be appreciated that more than one secondary cell may be sealed together by the protective sheet, thereby enabling one or more secondary cells to be comprised in the same pocket.

Still in the first state, the barrier formed by the protective sheet between the venting channel and each failure vent provides the advantage of protecting those failure vents from ejecta generated during thermal failure of a neighboring cell and carried through the venting channel by the gases. As used herein, “barrier” may be understood as a physical separation preventing, or at least limiting, fluid communication. It will further be appreciated that the barrier provides the advantage of protecting the failure vents and their corresponding secondary cell from moisture resulting from the high temperature of the gases released from a neighboring cell experiencing thermal failure and carried through the venting channel. The barrier is therefore advantageous in that it provides protection against the combination of ejecta and moisture.

The sealing effect provided by the protective sheet and the barrier it forms thereby enables protection of healthy secondary cells and their respective failure vents from gases and/or ejecta traveling through the venting channel. That is, gases and/or ejecta having been released through the failure vent of a secondary cell experiencing thermal failure and through the protective sheet assuming its second state above that secondary cell. It will be appreciated that more than one secondary cell may experience thermal failure simultaneously, for instance if those secondary cells are sealed together by the protective sheet.

In the second state, the protective sheet enables localized passage of the vented gases from the failure vent of the secondary cell experiencing thermal failure to the venting channel. That is, in the second state the sealing provided by the protective sheet and the barrier it forms above the secondary cell is ruptured in response to thermal failure occurring in said secondary cell, releasing the gases into the venting channel. It will be appreciated that where the protective sheet forms an at least partly sealed pocket above the failure vent, the rupture of the protective sheet when the protective sheet assumes the second state will effectively also rupture the pocket. It will further be appreciated that the protective sheet may assume the second state in those areas of the battery module in which the failure vent of a secondary cell is open due to thermal failure and simultaneously assume the first state in those areas of the battery module in which the failure vent of a secondary cell remains closed, i.e. those areas of the protective sheet covering healthy secondary cells.

The transition from the first state to the second state assumed by the protective sheet in response to opening of a failure vent thereby permits healthy secondary cells to remain protected by the barrier formed by the protective sheet all the while enabling gases generated in secondary cells incurring thermal failure to pass from their respective failure vents into the venting channel. Hence, the first state and second state assumed by the protective sheet reduce the risk of having gases released through the failure vent of a secondary cell experiencing thermal failure trigger thermal failure in other secondary cells when traveling throughout the battery module. It will be appreciated that the transition from first state to second state enables fluid communication between the failure vents of only those secondary cells experiencing thermal failure and the venting channel while at least partially isolating the remaining healthy secondary cells from the venting channel and from those secondary cells experiencing thermal failure.

Furthermore, the sealed pockets permit localized transition of the protective sheet from first to second state over the entire area covered by the protective sheet, i.e. over the failure vents of the plurality of secondary cells. The at least partially sealed pockets thereby also permit restricting the transition from first to second state to specific regions of the protective sheet, covering the failure vent of the one or more secondary cells experiencing thermal failure, therefore, the at least partially sealed pockets enable the protection of healthy secondary cells from gases released through the gas vent of damaged secondary cells and traveling through the venting channel. It will further be appreciated that said transition of the protective sheet from first state to second state may be enabled via various alternatives such as, but not limited to, rupturing, melting, ripping, bursting, etc.

For instance, according to an embodiment of the present disclosure, the protective sheet may be configured to rupture in response to the vented gases exerting a pressure, on the protective sheet, exceeding a predetermined threshold. This, especially in combination with the sealing effect of the protective sheet, enables pressure to build up only above those secondary cells experiencing thermal failure, thereby permitting a rapid pressure increase resulting in an early transition of the protective sheet from first state to second state. This in turn enables a quick response to thermal failure of secondary cells and a quick evacuation of gases generated therein out of the battery module. It will be appreciated that the predetermined threshold of pressure is dependent on the material forming the protective sheet and may therefore vary from one material to another.

For instance, according to an embodiment of the present disclosure, the protective sheet may be formed of a metal foil.

Alternatively, and according to an embodiment of the present disclosure, the protective sheet may be configured to break in response to the vented gases heating the protective sheet to a temperature exceeding a predetermined threshold. This, especially in combination with the sealing effect of the protective sheet, enables transition of the protective sheet from its first state to its second state only above those secondary cells releasing gases due to thermal failure. The present embodiment thereby also provides a quick response to thermal failure and a quick evacuation of gases generated therein out of the battery module. It will be appreciated that the predetermined threshold of temperature is dependent on the material forming the protective sheet and may therefore vary from one material to another.

For instance, according to an embodiment of the present disclosure, the protective sheet may be formed of a polymeric material.

According to yet another embodiment of the present disclosure, the top cover may be configured to secure the protective sheet against the plurality of secondary cells. That is, the top cover permits sealing of the secondary cells, and therefore the sealing of the failure vents of those secondary cells. The top cover thereby enables the sealing effect of the protective sheet by ensuring its immobilization above the plurality of secondary cells. It will be appreciated that the top cover further provides structural stability to the battery module.

According to an embodiment of the present disclosure, the protective sheet may be integrally formed with the top cover, thereby providing the advantage of simplifying the assembly and disassembly of the battery module. The present embodiment further enables a lesser number of components forming the battery module.

Again according to an embodiment of the present disclosure, the top cover may comprise a plurality of perforations allowing the vented gases to pass therethrough. As used herein, “perforation” may be understood as any of, but not limited to, aperture, hole, opening, orifice, etc. The plurality of perforations provides a direction for the vented gases to travel through the protective sheet assuming its second state and into the venting channel. It will be appreciated that the number and size of the perforations be such that vented gases may pass substantially vertically therethrough with minimal obstruction from the structure of the top cover. It will be appreciated that there may alternatively be only one perforation which area covers the plurality of secondary cells and the protective sheet covering them.

According to an embodiment of the present disclosure, the venting channel defined by the top cover may be configured to guide the vented gases to a lateral side of the battery module. The plurality of perforations of the top cover thus provides a substantially vertical path for gases released from the secondary cell experiencing thermal failure and the venting channel it defines provides a lateral path for said gases to exit the battery module. In other words, the top cover and the venting channel it defines enable an upward-to-lateral flow path for vented gases permitting rapid evacuation of those gases from the battery module. It will be appreciated that the evacuation of vented gases out of the battery module may be done by means of, for example, an opening, a valve, a burst film covered opening, etc., positioned at the rear of the battery module and/or positioned at a lateral side of the battery module opposite the side in which the electrical connections between the battery module and the plurality of secondary cell are positioned.

According to an embodiment of the present disclosure, the battery module may comprise a support plate arranged above the top cover and configured to at least partly define the venting channel. The support plate is particularly advantageous for formations in which a plurality of battery modules is stacked on one another in that it enables the upward-to-lateral flow path for vented gases throughout the stacked formation. Still with respect to a stacked formation of battery modules, the support plate, according to a further embodiment of the present disclosure, may be configured to support a neighboring battery module stacked on top of the battery module to comprising that support plate.

Thus, according to a second aspect of the present disclosure, there is provided a battery pack comprising a stack of a plurality of battery modules as described above in reference to the first aspect. A collection, or pack, of battery modules stacked on one another increases the storage capacity of electrical energy thereby enabling the battery pack to be more effective in applications requiring longer sustained energy input. It will be appreciated that the electrical connections between each battery module of the pack and their respective plurality of secondary cells may be positioned on the same lateral side of the pack, or positioned on different lateral sides so as to alternate throughout the stacked configuration of the battery pack. The positioning of electrical connections may therefore be adapted to the specifications of the application in which the battery pack is used. It will further be appreciated that the opening through which vented gases are evacuated out of the battery pack may be positioned at the rear of the battery pack and common for each battery module. Alternatively, it will be appreciated that the opening may be positioned at the rear of each individual battery module forming the battery pack. It is further embodied that there may be a plurality of openings through which vented gases may exit the battery pack. Moreover, the distancing between the opening(s) through which vented gases are evacuated and the electrical connections provided by their respective positioning is advantageous in that it limits the interaction between the vented gases and the electrical connections, thereby limiting the risk of damaging the electrical connections.

Further objective of, features of, and advantages with the present invention will become apparent when studying the following detailed disclosure, the drawings, and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following. Brief description of drawings

One or more embodiments will be described, by way of example only, and with reference to the following figures, in which:

Figure 1a-b schematically show examples of a battery module with a top cover and protective sheet, according to embodiments of the present disclosure;

Figure 2a-d schematically show perspective views of a top cover and protective sheet wherein the top cover comprises various examples of perforations, according to an embodiment of the present disclosure;

Figure 3 schematically shows a top view of a battery module according to an embodiment of the present disclosure wherein at least one secondary cell is experiencing thermal failure;

Figure 4a-b schematically show cross-sectional views of a part of a battery module wherein the protective sheet assumes its first state and its second state respectively, according to an embodiment of the present disclosure; and

Figure 5 schematically shows a cross-sectional view of a part of a battery pack comprising a stack of a plurality of battery modules according to an embodiment of the present disclosure, wherein at least a secondary cell of one of the battery modules is experiencing thermal failure.

Detailed description

The present disclosure is described in the following by way of a number of illustrative examples. It will be appreciated that these examples are provided for illustration and explanation only and are not intended to be limiting on the scope of the disclosure.

Furthermore, although the examples may be presented in the form of individual embodiments, it will be recognized that the present disclosure also covers combinations of the embodiments described herein.

Figure 1a schematically shows an exploded view of a battery module 101 with a top cover 130 and a protective sheet 120, according to an embodiment of the present disclosure. The battery module 101 , as illustrated, may be formed of a plurality of cylindrical secondary cells 110 arranged in an alignment and contained by a modular frame 160. Each cylindrical secondary cell 110 may be held in a casing 111 wherein the casing 111 is shown comprising failure vents 112 for venting gases and/or evacuating ejecta released from each secondary cell if it experiences thermal failure.

The top cover 130 may embody a shape having a perimeter and area substantially similar to the perimeter and area formed by the plurality of cylindrical secondary cells 110 and by the modular frame 160 containing them, as illustrated, but it will be appreciated that the top cover may instead encompass a shape having a perimeter and area larger than the perimeter and area formed by the plurality of cylindrical secondary cells 110 and by the modular frame 160. The top cover 130 may further comprise a plurality of perforations 135 in its structure.

The protective sheet 120 is shown positioned between the plurality of secondary cells and the top cover in a vertical direction Y. The perimeter and area of the protective sheet 120 may be similar to that of the plurality of cylindrical secondary cells 110. The perimeter and area of the protective sheet 120 may also be similar to that of the top cover 130.

The battery module 101 is further shown comprising a support plate 140 positioned above the top cover 130 in the vertical direction Y and may be configured to support a subsequently arranged battery module (not shown), stacked on top of the battery module 101 in the vertical direction Y.

When the battery module 101 is assembled, the top cover 130 may secure the protective sheet 120 against the plurality of secondary cells 110. The protective sheet 120 may then extend above the plurality of cylindrical secondary cells 110 and cover the failure vents 112 of the cylindrical secondary cells 110. It will be appreciated that by covering the failure vents 112, it is here meant that there is an overlap between the area of the failure vents 112 and the surface area of the protective sheet 120 extending above the plurality of secondary cells 110. Amongst other advantages, the top cover 130 in an assembled battery module 101 enables the protective sheet 120 to form an at least partially sealed pocket above at one or more failure vents 112 of the plurality of cylindrical secondary cells 110. The at least partially sealed pocket may be formed by the protective sheet 120 being in contact with a top surface of the cylindrical secondary cell 110 surrounding the failure vent. Further, the top cover 130 in an assembled battery module 101 may be configured to receive the support plate 140 such that the top cover 130 defines a venting channel at least partially together with the support plate 140 for guiding the vented gases away from the plurality of cylindrical secondary cells 110.

It will be appreciated that the support plate 140 may comprise an opening 151 covered by a membrane 150 enabling pressure equalization between the venting channel and the surrounding the battery module 101 thereby reducing the risk of detrimental pressure increase in the battery module 101.

Figure 1 b schematically shows an exploded view of a battery module 102 characterized similarly as the battery module 101 illustrated in figure 1a, but comprising a plurality of prismatic secondary cells 110. The illustrated embodiment shows the prismatic secondary cells 110 arranged in an alignment and contained by the modular frame 160. Each prismatic secondary cell 110 may comprise a casing 111 and a failure vent 112 in said casing for venting gases and/or evacuating ejecta released from the prismatic secondary cell if it experiences thermal failure. It is to be noted that the perforations 135 comprised in the top cover 130 illustrated in figure 1 b embody a shape and size adapted to the prismatic secondary cells 110 and failure vents 112, which may differ from the shape and size embodied by the perforations depicted in figure 1a in relation to cylindrical secondary cells.

Figure 2a-d schematically show perspective views of a top cover 230 and a protective sheet 220 wherein the top cover 230 comprises various examples of perforations 235 according to embodiments of the present disclosure. The embodiment illustrated in figure 2a is characterized similarly as the top cover 130 and protective sheet 120 shown in figure 1 . The top cover 230 may be formed of a monolithic frame 234 which may be obtained by, but not limited to, an injection molding process, and may comprise a plurality of perforations 235. The perforations 235 illustrated in this embodiment are evenly distributed over the surface area of the top cover 230 such that at least one perforation 235 is positioned over the gas vent of each of the secondary cells of the battery module when assembled. The illustrated embodiment further shows the protective sheet 220 positioned under the top cover 230 enabling the top cover 230 to secure the protective sheet against the plurality of secondary cells when the battery module is assembled.

It will be appreciated that the protective sheet 220 may also be positioned above the top cover 230, as illustrated in figure 2b, without compromising the sealing and securing of the protective sheet 220 on the plurality of secondary cells provided by the top cover 230.

It will further be appreciated that the number of perforations 235 and size, or area, of the perforations 235 may embody different alternatives. For instance, figure 2c illustrates an embodiment of a top cover 231 wherein the frame 234 may comprise a plurality of perforations 235 having a larger area and being fewer in number than the embodiment shown in figures 2a-2b. The area of the perforations 235 of top cover 231 may each cover a plurality of failure vents of secondary cells which may enable the protective sheet 220 to form a sealed pocket over more than one secondary cell.

Alternatively, the top cover 232 depicted in figure 2d comprises a singular perforation 235 in its frame 234, wherein the area of the singular perforation 235 may cover the plurality of secondary cells when the battery module is assembled. It will be appreciated that the area of the singular perforation 235 of top cover 232 may be sized and shaped such that the structural strength of the frame 234 of the top cover 232 remains adequate for supporting the support plate when the battery module is assembled, as well as neighboring battery modules when considering a stacked formation for a plurality of battery modules.

Still further, it will be appreciated that the protective sheet 220 in any of the figures 2a-d may be integrally formed with the top cover 230.

Figure 3 schematically shows a top view of a battery module 300 according to an embodiment of the present disclosure wherein at least one secondary cell 310 is experiencing thermal failure, exemplified in figure 3 by a drawing of flames. For illustrative purposes, the support plate is not shown in figure 3. The battery module 300 is shown comprising a top cover 330 having a plurality of perforations 335, each perforation 335 comprising an area covering at least one failure vent 312 of secondary cells 310.

The top cover 330 is further depicted securing the protective sheet 320 on the plurality of secondary cells 312 such that partially sealed pockets may be formed by the protective sheet 320 above the failure vents 312 within the area provided by each perforation 335. The illustrated embodiment further shows the protective sheet 320 assuming a first state 321 in which it forms a barrier between the failure vents 312 of the secondary cells 310 it covers and the venting channel (not shown).

Still further, the protective sheet 320 covering at least one secondary cell 310 experiencing thermal failure is shown assuming the second state 322 in which passage of vented gases from the failure vent 312 of the secondary cell experiencing thermal failure to the venting channel is enabled.

The secondary cells 310 covered and at least partially sealed by the protective sheet 320 assuming the first state 321 may therefore be isolated from the at least one secondary cell 310 experiencing thermal failure and being covered by the protective sheet 320 assuming the second state 322, which may advantageously reduce the risk of spreading of the thermal failure from the affected secondary cell 310 to neighboring healthy secondary cells 310.

Figure 4a-b schematically show cross-sectional views of a part of a battery module 401 , 402 wherein the protective sheet 420 assumes its first state 421 and its second state 422 respectively, according to an embodiment of the present disclosure. The embodiment illustrated in figure 4a depicts a section of the battery module 401 comprising a plurality of secondary cells 410 arranged in an alignment. The illustrated embodiment depicts the protective sheet 420 assuming its first state 421 and forming a barrier between the failure vents 412 and the venting channel 470 defined by the top cover 430 and at least partially by the support plate 440. It will be appreciated that each secondary cell 410 illustrated in figure 4a may represent healthy secondary cells 410, i.e. secondary cells unaffected by thermal failure and for which failure vents 412 remain closed. Upon thermal failure occurring in at least one secondary cell 410, the failure vent 413 of the damaged secondary cell 415 may be configured to open, as depicted by the section of battery module 402 illustrated in figure 4b. The illustrated embodiment further shows the protective sheet 420 assuming its second state 422 enabling passage of gases 480, generated by the thermal failure of the secondary cell 415, from the failure vent 413 to the venting channel 470. It will be appreciated that the support plate 440 is shown slightly elevated from the top cover 430 for illustrative purposes.

It will be appreciated that the protective sheet 420 may transition from the first state to the second state 422 by being ruptured due to local overpressure on an area of the protective sheet 420 aligned with the area provided by one or more perforations comprised in the top cover 430. It will further be appreciated that this transition may occur due to local heating of the protective sheet 420 at an area thereof aligned with the area provided by one or more perforations comprised in the top cover 430.

Furthermore, the failure vent 413 and the venting channel 470 depicted in figure 4b are shown providing an upward-to-lateral flow path for vented gases 480 leading the gases 480 away from the remaining healthy secondary cells 410 and out of the battery module.

Figure 5 schematically shows a cross-sectional view of a part of a battery pack 500 comprising a stack of a plurality of battery modules 501 , 502, 503 according to an embodiment of the present disclosure, wherein at least one secondary cell 515 of one of the battery modules 502 is experiencing thermal failure. The battery modules 501 , 502, 503 are shown stacked in a vertical arrangement wherein the support plate 540 of battery modules 501 , 502 may be configured to support the neighboring battery modules 502, 503 stacked on top thereof. The illustrated embodiment further depicts the upward-to-lateral flow path taken by the vented gases 580 through the open failure vent 513 and venting channel 570. The venting channel 570 may therefore be configured to evacuate vented gases 580 away from the healthy secondary cells 510 and away from the support plate 570 of the neighboring battery module 503 so as to avoid, or at least limit, spreading of thermal failure within the secondary cells 510 of the affected battery module 502 and within the neighboring battery module 503 stacked on top thereof. In a stacked formation such as the one embodied by the battery pack 500, the evacuation of vented gases 580 out of the battery pack 500 may be performed through an opening (not shown), common for each battery module 501 , 502, 503 and positioned at the back of the battery pack 500. It will be appreciated that the evacuation of vented gases 580 out of the battery pack 500 may alternatively be performed through openings (not shown) positioned at the back of each individual battery module 501 , 502, 503 forming the battery pack 500. It will be appreciated that, although the above aspects are presented separately, they may be combined in any suitable manner such that a battery pack may benefit from all of the advantages provided by respective aspects of the present disclosure.

Furthermore, whilst the forgoing description and the appended drawings are provided as exemplary or preferred realizations of the disclosed aspects, it will be appreciated that the disclosed aspects need not be limited to the exact form shown and/or described.

Claims

1 . A battery module (100, 300,401 , 402) comprising: a plurality of secondary cells (110, 310, 410, 510), each secondary cell of the plurality of secondary cells having a casing (111 ) and a failure vent (112, 312, 412, 413, 512, 513) in the casing for venting gases (480, 580) upon thermal failure of the secondary cell; a protective sheet (120, 220, 320, 420) extending above the plurality of secondary cells and arranged to cover the failure vents; and a top cover (130, 230, 330, 430) configured to define a venting channel (470, 570) for guiding the vented gases away from the cell; wherein the protective sheet is configured to assume a first state (321 , 421 ) in which it forms a barrier between the failure vent and the venting channel, and a second state (322, 422) in which it enables passage of the vented gases from the failure vent to the venting channel; and wherein the protective sheet is configured to transition from the first state to the second state in response to opening of the failure vent.

2. The battery module according to claim 1 , wherein the protective sheet is configured to rupture in response to the vented gases exerting a pressure, on the protective sheet, exceeding a predetermined threshold.

3. The battery module according to claim 2, wherein the protective sheet is formed of a metal foil.

4. The battery module according to claim 1 or 2, wherein the protective sheet is configured to break in response to the vented gases heating the protective sheet to a temperature exceeding a predetermined threshold.

5. The battery module according to claim 2 or 4, wherein the protective sheet is formed of a polymeric material.

6. The battery module according to any of the preceding claims, wherein the protective sheet is configured to form an at least partly sealed pocket above at least one of the failure vents.

7. The battery module according to any of the preceding claims, wherein the top cover is configured to secure the protective sheet against the plurality of secondary cells.

8. The battery module according to any of claims 1-6, wherein the protective sheet is integrally formed with the top cover.

9. The battery module according to any of the preceding claims, wherein the top cover comprises a plurality of perforations (135, 235, 335) allowing the vented gases to pass therethrough.

10. The battery module according to any of the preceding claims, wherein the venting channel is configured to guide the vented gases to a lateral side of the module.

11 . The battery module according to any of the preceding claims, further comprising a support plate (140, 440, 540) arranged above the top cover and configured to at least partly define the venting channel.

12. The battery module according to claim 11 , wherein the support plate is further configured to support a neighboring module (501 , 502, 503) stacked on top of the module.

13. A battery pack (500) comprising a stack of a plurality battery modules according to any of the preceding claims.