TRACTION BATTERY PACK VENTILATION SYSTEM WITH DETACHABLE SHIELDING FOR COATED AREA

Abstract

A traction battery pack venting system comprises one or more battery cells and a venting chamber adjacent to the one or more battery cells. The one or more battery cells are configured to vent into the venting chamber. A releasable shield is moved from an attached position to a detached position by venting byproducts expelled from one or more battery cells. A guide system restricts movement of the releasable shield when it is in the detached position.

Description

AREA OF TECHNOLOGY This disclosure relates generally to a venting system for a battery pack and more specifically to a venting system for a battery pack that shields coated areas, such as electroplated areas, of the battery pack from venting by-products. GENERAL STATE OF THE ART Electrified vehicles differ from conventional motor vehicles in that they can be selectively powered by one or more electric motors, which are supplied with power by a traction battery pack. These electric motors can power the electrified vehicles instead of, or in combination with, an internal combustion engine. The traction battery pack is discharged when the one or more electric motors and other electrical consumers of the electrified vehicle are being powered. SUMMARY In some aspects, the techniques described in this document relate to a traction battery pack venting system comprising: one or more battery cells; a venting chamber adjacent to the one or more battery cells, wherein the one or more battery cells are configured to vent into the venting chamber; a releasable shield that is moved from an attached position to a detached position by venting byproducts ejected from one or more battery cells; and a guidance system that restricts movement of the releasable shield when the releasable shield is in the detached position. In some aspects, the techniques described in this document relate to a traction battery pack venting system, which further includes a wall of the battery pack, wherein the one or more battery cells are each configured to vent a stream of venting by-products towards the wall, and wherein the guidance system is configured to hold the releasable shield in a position between the stream of venting by-products and the wall. In some aspects, the techniques described in this document relate to a traction battery pack venting system, where the wall is at least partially electroplated. In some aspects, the techniques described in this document relate to a traction battery pack venting system, where the wall is an outer wall of an enclosure. In some aspects, the techniques described in this document relate to a traction battery pack venting system, wherein at least the outer wall is a coated metal or a coated metal alloy. In some aspects, the techniques described in this document relate to a traction battery pack venting system, where one or more battery cells are immersion cooled. In some aspects, the techniques described in this document relate to a traction battery pack venting system, where one or more battery cells are cylindrical battery cells. In some aspects, the techniques described in this document relate to a traction battery pack venting system, wherein the venting chamber is sealed against a cell chamber enclosing the one or more battery cells in such a way as to prevent a fluid, which is passed through the cell chamber as part of an immersion heat regulation system, from entering the venting chamber. In some aspects, the techniques described in this document relate to a traction battery pack venting system, which further includes a cell carrier having a platform that supports the one or more battery cells. In some aspects, the techniques described in this document relate to a traction battery pack venting system, wherein the detachable shielding includes a piece of thermal shielding located adjacent to the platform. In some aspects, the techniques described in this document relate to a traction battery pack venting system, wherein the platform includes a plurality of vent openings, wherein the one or more battery cells are each configured to vent into the venting chamber through at least one of the vent openings within the plurality of vent openings. In some aspects, the techniques described in this document relate to a traction battery pack venting system, wherein the guidance system includes a plurality of fingers, each extending from the platform into the venting chamber, the plurality of fingers each being arranged around at least one of the vent openings within the plurality of vent openings. In some aspects, the techniques described in this document relate to a traction battery pack venting system, wherein the removable shielding includes a section of a container of the respective battery cell. In some aspects, the techniques described in this document relate to a traction battery pack venting system, which further includes a cell carrier having a platform supporting the one or more battery cells, the platform including a plurality of vent openings, the one or more battery cells each being configured to vent through one or more of the vent openings into the venting chamber, the releasable shield being configured to pass through one of the vent openings in the detached position. In some aspects, the techniques described in this document relate to a traction battery pack venting system, with the detachable shield further incorporating a piece of thermal shielding. In some aspects, the techniques described in this document relate to a traction battery pack venting system, where the heat shielding is a mica film. In some aspects, the techniques described in this document relate to a battery pack shielding procedure that involves: venting a battery cell into a venting chamber; during venting, transferring a removable shield from an attached position to a detached position; and restricting movement of the removable shield during venting. In some aspects, the techniques described in this document relate to a battery pack shielding method, which further involves regulating thermal energy using a liquid coolant, wherein the battery cell is at least partially immersed in the liquid coolant. In some aspects, the techniques described in this document relate to a battery pack shielding method wherein the movement of the removable shield is restricted in order to hold the removable shield in a position in which the removable shield prevents a stream of venting by-products from striking a section of a wall of an enclosure in which the battery cell is housed. In some aspects, the techniques described in this document relate to a battery pack shielding method, where the wall is at least partially electroplated. The embodiments, examples, and alternatives described in the preceding paragraphs, the claims, or the following description and drawings, which may include any of their various aspects or individual features, can be considered independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, provided such features are not incompatible. BRIEF DESCRIPTION OF THE FIGURES The various features and advantages of the disclosed examples will become apparent to the person skilled in the art from the detailed description. The figures accompanying the detailed description can be briefly described as follows: Fig. 1 illustrates a side view of an electrified vehicle having a battery pack. Fig. 2 illustrates a perspective view of a battery cell from the battery pack of Fig. 1. Fig. 3 illustrates another perspective view of the battery cell from Fig. 2 when the battery cell is vented. Fig. 4 illustrates a perspective view of the battery pack from the electrified vehicle of Fig. 1 according to an exemplary embodiment of the present disclosure. Fig. 5 illustrates an expanded view of the battery pack from Fig. 4. Fig. 6 illustrates a sectional view along line 6-6 in Fig. 4.Figure 7 illustrates a bottom view of a section of the cell carrier. DETAILED DESCRIPTION This disclosure describes in detail exemplary traction battery packs with venting systems. The venting systems may include a venting chamber. During a thermal event, battery cells can vent into the venting chamber. A removable shield can prevent venting byproducts emitted by one or more battery cells from directly impacting the outer wall, which may be coated. Referring to Fig. 1, an electrified vehicle 10 includes a battery pack 14, an electric motor 18, and wheels 22. The battery pack 14 supplies the electric motor 18 with power, which can convert electrical power into mechanical power to drive the wheels 22. The battery pack 14 is thus a traction battery pack. In the exemplary embodiment, the battery pack 14 is secured to an underbody 26 of the electrified vehicle 10. In other examples, the battery pack 14 could be located elsewhere on the electrified vehicle 10. The electrified vehicle 10 is a fully electric vehicle. In other examples, the electrified vehicle 10 is a hybrid electric vehicle that selectively drives wheels using torque provided by an internal combustion engine instead of, or in addition to, an electric motor. Generally, the electrified vehicle 10 could be any type of vehicle that incorporates a traction battery pack. Now, with reference to Figures 2 and 3, the battery pack 14 of the exemplary embodiment comprises a plurality of battery cells 34. In this example, the battery cells 34 are cylindrical lithium-ion battery cells. In particular, the exemplary battery cells 34 each have a round-wound electrode structure housed within a container 38. The cylindrical battery cells 34 are each arranged along a corresponding battery cell axis A. A cap 42 of the container 38 provides a positive terminal at a first axial end of each cell 34. The cap 42 is raised above a ring 44, which provides a negative terminal at the first axial end of each cell 34. Busbars can be connected to the terminals provided by the caps 42 and rings 44 of the cells 34 to electrically couple the cells 34 to other cells 34, to other components of the battery pack 14, or both. The busbars are omitted from the figures. A vent side 46 of the container 38 is located at an opposite, second axial end of each cell 34. The container 38 includes a removable shield 48 on the vent side 46. The container 38 may be thinned around the circumference of the removable shield 48 to form an outer circumference of the removable shield 48. During a thermal event in one of the cells 34, pressure increases can separate the detachable shield 48 from the other sections of the vessel 38. In particular, the increased pressure can rupture the vessels 38 at the thinned areas, which can cause the detachable shield 48 to be transferred from a fixed position to a detached position. The transfer of the detachable shield 48 to the detached position provides an opening 50 in the vessel 38. Vent byproducts V can then pass through the opening 50. Now, with reference to Figs. 4-7 and further reference to Figs. 1-3, in the exemplary battery pack 14 the batteries 34 are housed in an interior space 52 of an enclosure assembly 56. In the exemplary embodiment, the enclosure assembly 56 comprises an enclosure cover 60 and an enclosure shell 64. The enclosure cover 60 can be secured to the enclosure shell 64 to provide the interior space 52 in which the battery cells 34 are housed. The enclosure cover 60 can, for example, be secured to the enclosure shell 64 using mechanical fasteners (not shown). Within the interior space 52, the battery cells 34 are supported on a platform 72 of a cell carrier 74. Supports 76 of the cell carrier 74 extend downwards from the platform 72 to a base 80 of the casing shell 64, raising the platform 72 above the base 80 within the interior space 52. The platform 72 divides the interior space 52 into a cell chamber 84 and a vent chamber 88. The cell carrier 74 can be made of a polymer-based material reinforced with glass fibers. The exemplary battery pack 14 regulates the thermal energy of the battery cells 34 and other components of the battery pack 14 using a liquid coolant. The cells 34 and other components of the battery pack 14 are at least partially immersed in the liquid coolant. The thermal energy within the battery pack 14 is thus regulated using an immersion thermal control system. In other examples, instead of being immersed in the liquid coolant, the battery cells 34 could be arranged adjacent to a heat exchanger plate, and the liquid coolant could be passed through the heat exchanger plate to regulate the thermal energy of the battery cells 34. In this example, the liquid coolant cools the battery cells 34 and the other components of the battery pack 14. In another example, the liquid coolant could be used instead or additionally to heat the battery cells 34 and the other components. The liquid coolant could, for example, be a dielectric coolant. In this example, a pump 92 circulates the liquid coolant through the cell chamber 84. The platform 72 prevents the liquid coolant from entering the vent chamber 88. The battery cells 34 are enclosed within the cell chamber 84. Within cell chamber 84, the liquid coolant flows over the battery cells 34 and other components, absorbing heat energy from them. The liquid coolant then moves from the battery pack 14 to a heat exchanger 96. Heat energy can be dissipated from the liquid coolant at the heat exchanger 96. The liquid coolant moves from the heat exchanger 96 to a liquid supply 100. The liquid coolant is drawn from the liquid supply 100 as needed and circulated back to the battery pack 14 by the pump 92. Platform 72 separates the vent chambers 88 from the cell chamber 84 in such a way that liquid coolant, which is routed through the cell chamber 84 as part of the immersion heat regulation system, is prevented from entering the vent chamber 88. The vent chamber 88 is sealed off from the cell chamber 84. The battery pack 14 includes a vent 104 within the casing shell 64. Venting byproducts V, released from one or more of the battery cells 34 into the vent chamber 88, can escape from the casing assembly 56 through the vent 104. Venting byproducts V, absorbed within the vent chambers 88, can flow through the vent 104 to the gap G. The venting chamber 88 is adjacent to the battery cells 34. To provide passage to the venting chamber 88, the platform 72 includes a plurality of vent openings 108. Each vent opening 108 is aligned with one of the removable shields 48 for each of the battery cells 34. If one of the battery cells 34—here, battery cell 34A in Fig. 6—experiences a thermal event, the venting byproducts V can detach the removable shield 48 from other sections of the container 38 and force the removable shield 48 through the associated vent opening 108 into the venting chamber 88. The venting byproducts V also move through the vent opening 108 into the venting chamber 88. The enclosure assembly 56 can be made of a metal or a metal alloy, such as steel. The enclosure assembly 56 can be coated with a coating, such as a coating that prevents the enclosure assembly 56 from rusting. Both the outer and inner surfaces of the enclosure assembly 56 can be coated with the coating, which in some examples is an electrolytic coating. In some examples, the platform 72 and the stands 76 can also be coated. To shield coated areas from the venting byproducts, the exemplary battery pack 14 includes a guidance system 112 that restricts the movement of the removable shield 48, which has been detached from the other sections of the container 38 by the venting byproducts. In this example, the guidance system 112 is provided by a plurality of fingers 116 extending from the platform 72 into the venting chamber 88. The fingers 116 can extend to the bottom 80 or terminate just short of the bottom 80. In these examples, four fingers 116 are distributed around each of the ventilation openings 108. Other examples could involve a different number of fingers 116 distributed around the ventilation openings 108. When the releasable shield 48 is in the detached position and is pushed through the vent opening 108 by the venting by-products, the fingers 116 essentially provide a cage that restricts the movement of the releasable shield 48. In this example, the battery cells 34 are vertically oriented and configured to vent downwards towards the vent chamber 88. For the purposes of this disclosure, vertical refers to the ground and a general orientation of the battery pack 14 when installed inside the vehicle 10. The fingers 116 prevent the removable shield 48 from moving horizontally away from an area below the vent 108. The fingers 116 hold the removable shield 48 in a position between the stream of venting byproducts V and the encapsulation assembly 56. The venting byproducts V thus contact the removable shield 48 instead of directly impacting the encapsulation assembly 56. Since the venting byproducts can have a relatively high temperature, preventing the venting byproducts V from impacting the encapsulation assembly 56 can reduce the amount of thermal energy introduced into the encapsulation assembly 56 and its coating. This can help to suppress any thermal event associated with the coating on the encapsulation assembly 56. In this example, the removable shield 48 is part of the container 38. In other examples, the removable shield 48 could instead or additionally be a thermal barrier separate from the battery cells 34. For example, a thermal barrier film, such as a mica film, could cover the platform 72 and span the openings 108. The cells 34 can rest on the thermal barrier film. The thickness of the thermal barrier film can be from 0.4 to 4 millimeters. The thermal barrier film may contain perforations in the areas of the openings 108. During a venting event, the venting byproducts expelled from one or more of the battery cells 34 may tear the thermal barrier film at the perforations, causing a piece of the thermal barrier film to detach from the surrounding areas. The venting byproducts may then push the detached piece through the respective opening 108. The guide system 112 limits the horizontal movement of the detached piece. The detached piece of the heat barrier film remains below the vent opening 108 and shields the encapsulation assembly 56 and any coating from direct contact with the venting byproducts. In such an example, the detached piece of the heat barrier provides the removable shield. In other examples, the detachable shielding could be provided by a piece of a thermal barrier and a section of the container 38 of one of the cells 34. Features of the disclosed examples include shielding an enclosure from a direct stream of venting by-products using a shield that is held in a shielding position by a guidance system. The preceding description is exemplary and not limiting. Variations and modifications of the disclosed examples may be apparent to a person skilled in the art, which do not necessarily deviate from the core of this disclosure. Therefore, the scope of protection granted by this disclosure can only be determined by reading the following patent claims.

Claims

Traction battery pack venting system comprising: one or more battery cells; a venting chamber adjacent to the one or more battery cells, wherein the one or more battery cells are configured to vent into the venting chamber; a releasable shield which is moved from an attached position to a detached position by venting by-products ejected from one or more battery cells; and a guidance system which restricts movement of the releasable shield when the releasable shield is in the detached position. Traction battery pack venting system according to claim 1, further comprising a wall of the battery pack, wherein the one or more battery cells are each configured to vent a stream of venting by-products towards the wall, wherein the guidance system is configured to hold the releasable shield in a position between the stream of venting by-products and the wall, and wherein optionally the wall is at least partially electroplated. Traction battery pack venting system according to claim 2, wherein the wall is an outer wall of a container, and wherein optionally at least the outer wall is a coated metal or a coated metal alloy. Traction battery pack venting system according to claim 1, wherein the one or more battery cells are immersion cooled. Traction battery pack venting system according to claim 1, wherein the one or more battery cells are cylindrical battery cells. Traction battery pack venting system according to claim 1, wherein the venting chamber is sealed against a cell chamber enclosing the one or more battery cells in such a way that a fluid which is passed through the cell chamber as part of an immersion heat regulation system is prevented from entering the venting chamber. Traction battery pack venting system according to claim 1, further comprising a cell carrier having a platform supporting the one or more battery cells, and wherein optionally the releasable shielding comprises a portion of a heat shield arranged adjacent to the platform. Traction battery pack venting system according to claim 7, wherein the platform includes a plurality of vent openings, wherein the one or more battery cells are each configured to vent through at least one of the vent openings within the plurality of vent openings into the venting chamber, and wherein optionally the guide system includes a plurality of fingers, each extending from the platform into the venting chamber, the plurality of fingers each arranged around at least one of the vent openings within the plurality of vent openings. Traction battery pack venting system according to claim 1, wherein the detachable shield includes a section of a container of the respective battery cell. Traction battery pack venting system according to claim 9, further comprising a cell carrier having a platform supporting the one or more battery cells, the platform comprising a plurality of vent openings, the one or more battery cells each being configured to vent through one or more of the vent openings into the venting chamber, the releasable shield being configured to pass through one of the vent openings in the detached position. Traction battery pack venting system according to claim 10, wherein the detachable shield further comprises a piece of a heat shield, and wherein the heat shield is optionally a mica film. Battery pack shielding method, comprising: venting a battery cell into a venting chamber; during venting, transferring a detachable shield from an attached position to a detached position; and restricting movement of the detachable shield during venting. Battery pack shielding method according to claim 12, further comprising regulating thermal energy using a liquid coolant, wherein the battery cell is at least partially immersed in the liquid coolant. Battery pack shielding method according to claim 12, wherein the movement of the releasable shield is restricted in order to keep the releasable shield in a position in which the releasable shield prevents a stream of venting by-products from striking a section of a wall of an enclosure in which the battery cell is housed. Battery pack shielding method according to claim 14, wherein the wall is at least partially electroplated.

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