Evacuation vent

Abstract

There is herein provided a vent assembly comprising a membrane (4) and a vent stack, the vent stack comprising an adhesive layer (2), wherein the vent stack is configured to fail during use when the pressure differential across the vent assembly when the vent assembly is installed across an aperture defined in a battery housing is greater than a threshold pressure, wherein the threshold pressure is at least 5 kPa.

Description

[0001] Evacuation Vent

[0002] Field

[0003] The present disclosure relates to the field of vents for battery packs, specifically to vents or vent assemblies for battery packs and battery packs comprising the same.

[0004] Background

[0005] Lithium-ion batteries are used for propulsion of electric vehicles and for energy storage systems including residential and commercial energy storage systems. Batteries for passenger vehicles can store on the order of 100 kWh of energy, and original equipment manufacturers (OEMs) are always working to increase energy density of the battery pack to improve vehicle range. On rare occasions, individual battery cells can enter thermal runaway, due to manufacturing defects which induce a short, external trauma such as a crash, or overheating of the cell. When thermal runaway occurs, a large amount of gas can be produced by the battery cell (or, in the case of thermal propagation to adjacent cells, multiple cells) in a short period of time. This rapid gas generation can quickly overwhelm the ability of the pressure equalization vents on the battery pack to release the gas. It is for this reason that OEMs and battery pack manufacturers install emergency evacuation vents, which can burst, rupture, or otherwise open to create a large diameter orifice through which the gases generated by a thermal runaway event can flow unimpeded.

[0006] Evacuation vents have traditionally consisted of molded plastic parts with internal membranes or valves of some sort. These components are typically large, relative to the sizes of the holes they protect, which limits the locations on the battery pack (or battery module) where they can be installed. These components are also relatively expensive, in an industry that is always looking to reduce cost.

[0007] While thermal runaway is primarily an issue for electric vehicle batteries, thermal runaway can also occur in small portable devices such as cordless power tools and other similar battery- powered devices as well as energy storage systems.

[0008] Accordingly, there remains a need for improved vents and vent assemblies for use as evacuation vents.

[0009] At least some aspects of the present disclosure are aimed to provide improved vents, vent assemblies and battery packs comprising improved vent assemblies. Summary

[0010] According to a first aspect there is provided a vent assembly comprising a membrane and a vent stack, the vent stack comprising an adhesive layer, wherein the vent stack is configured to fail during use when the pressure differential across the vent assembly when the vent assembly is installed across an aperture defined in a battery housing is greater than a threshold pressure.

[0011] For the avoidance of doubt, the pressure differential across the vent assembly is the difference between the pressure on a first side of the vent assembly and the pressure on a second side of the vent assembly. When the vent assembly is installed over an evacuation aperture of a battery pack housing or a battery cell housing the pressure differential across the vent assembly is the difference between the pressure within the battery pack housing or a battery cell housing and the pressure outside the battery pack housing or a battery cell housing.

[0012] The vent assembly may be configured to act as a release valve or release vent. During use when the vent assembly is installed across an aperture defined in a battery housing, when the pressure differential across the vent assembly is less than the threshold pressure, the vent assembly allows airflow across the vent assembly to thereby equalise the pressure within the battery housing. When the pressure differential across the vent assembly is greater than the threshold pressure the vent stack fails to thereby increase the permitted flow of gas through the aperture.

[0013] A vent assembly that is configured to fail when the pressure differential across the vent assembly is greater than a threshold pressure ensures that the vent may act as an evacuation vent to ensure that a potentially dangerous build-up of pressure within a battery housing is prevented.

[0014] The vent stack may be configured to fail during use at the interface between the adhesive layer and the membrane. The vent stack may be configured to fail during use at the interface between the adhesive layer and the battery housing.

[0015] Typically, the vent stack defines an aperture such that during use gas may pass through the aperture of the vent stack to and from the membrane. Accordingly, the vent stack may have an inner edge adjacent defining the aperture of the vent stack and an outer edge and the adhesive layer may have an inner edge and an outer edge. The threshold pressure may be at least 5 kPa. The threshold pressure may be at least 7 kPa. The threshold pressure may be at least 10 kPa. The threshold pressure may be at least 15 kPa. The threshold pressure may be at least 20 kPa.

[0016] The threshold pressure may be from 5 kPa to 300 kPa. The threshold pressure may be from 7 kPa to 300 kPa. The threshold pressure may be from 10 kPa to 300 kPa. The threshold pressure may be from 15 kPa to 300 kPa. The threshold pressure may be from 20 kPa to 300 kPa. The threshold pressure may be from 5 kPa to 250 kPa. The threshold pressure may be from 5 kPa to 200 kPa. The threshold pressure may be from 5 kPa to 150 kPa. The threshold pressure may be from 5 kPa to 100 kPa.

[0017] The vent stack of the vent assembly may be configured to fail above the threshold pressure consistently. The vent stack of the vent assembly may be configured to fail when the pressure differential across the vent assembly is less than 20 kPa above the threshold pressure. The vent stack of the vent assembly may be configured to fail when the pressure differential across the vent assembly is less than 15 kPa above the threshold pressure. The vent stack of the vent assembly may be configured to fail when the pressure differential across the vent assembly is less than 10 kPa above the threshold pressure. The vent stack of the vent assembly may be configured to fail when the pressure differential across the vent assembly is less than 5 kPa above the threshold pressure.

[0018] In some embodiments, the adhesive layer may be configured to fail. The adhesive layer may comprise a substrate and an adhesive may be provided on each major surface of the substrate to form a first adhesion surface and a second adhesion surface. The adhesive layer may be configured to adhere the vent stack to the membrane. The adhesive layer may be configured to adhere the vent assembly to a battery pack housing. The adhesive layer may be configured to fail when the pressure differential across the vent assembly is greater than the threshold pressure by the failure of the first adhesion surface or the second adhesion surface. The adhesive layer may be configured to fail when the pressure differential across the vent assembly is greater than the threshold pressure by the failure of the interface between the first adhesion surface and a substrate, or the failure of the interface between the second adhesion surface and a substrate. For example, the substrate may be the membrane of the vent assembly or a battery housing wall of a battery pack onto which the vent assembly is installed during use. The adhesive layer may comprise an adhesive layer weak point and during use the adhesive layer may be configured to fail at the weak point when the pressure differential across the vent assembly is greater than the threshold pressure. The adhesive layer weak point may be located on the inner edge of the adhesive layer. The adhesive layer weak point may be located on the outer edge of the adhesive layer.

[0019] The adhesive layer weak point may correspond to a portion of the adhesive layer that has weaker adhesion than the remainder of the adhesive layer. The adhesive layer weak point may comprise a different adhesive to the remainder of the adhesive layer. The adhesive layer weak point may correspond to a thinner portion of the adhesive layer that is thinner than the remainder of the adhesive layer. The thinner portion may be adjacent to the inner edge of the adhesive layer. The adhesive layer weak point may comprise at least 5% of the inner edge of the adhesive layer. The adhesive layer weak point may comprise at least 10% of the inner edge of the adhesive layer. The adhesive layer weak point may comprise at least 15% of the inner edge of the adhesive layer. The thinner portion may be adjacent to the outer edge of the adhesive layer. The adhesive layer weak point may comprise at least 5% of the outer edge of the adhesive layer. The adhesive layer weak point may comprise at least 10% of the outer edge of the adhesive layer. The adhesive layer weak point may comprise at least 15% of the outer edge of the adhesive layer.

[0020] The adhesive layer weak point may correspond to a discontinuity in the adhesive layer.

[0021] The adhesive layer may extend around the perimeter of the membrane. The adhesive layer may have a width from the edge of the vent assembly towards the interior of the vent assembly. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer having a reduced width. Accordingly, the discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is at least 30% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is at least 40% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is at least 50% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is from 20% to 70% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is from 30% to 70% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is from 40% to 70% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is from 50% to 70% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is from 20% to 60% less than the width of the adhesive of the remainder of the adhesive layer. The discontinuity in the adhesive layer may correspond to a portion of the adhesive layer that has a width of adhesive that is from 20% to 50% less than the width of the adhesive of the remainder of the adhesive layer.

[0022] The discontinuity in the adhesive layer may comprise a failure point. The failure point may allow the location of the failure of the vent stack to be pre-determined. For example, the discontinuity may have a shape that has a point at the thinnest extent of the adhesive of the discontinuity such that the point is predisposed to be the point at which the adhesive layer fails.

[0023] The discontinuity may have a substantially geometric shape. The discontinuity may be substantially triangular. The discontinuity may be substantially rectangular or square. The discontinuity may be substantially pentagonal.

[0024] The adhesive layer may comprise a pressure sensitive adhesive. The adhesive layer may comprise an adhesive chosen from acrylic, silicone, rubber-based adhesive or a combination thereof. The adhesive layer may comprise a curable adhesive. The curable adhesive may be curable by exposure to heat. The curable adhesive may be curable by exposure to ultraviolet light.

[0025] The vent stack may further comprise a failure layer and the failure layer may be configured to fail when the pressure differential across the vent assembly is greater than the threshold pressure. The failure layer of the vent stack may be positioned between the adhesive layer and the membrane. The failure layer may be fixed to the membrane. The failure layer may be fixed to the membrane via a weld, for example. The vent stack may comprise a first adhesive layer and a second adhesive layer. The first adhesive layer may be positioned between the failure layer and the membrane. The second adhesive layer may be positioned between the failure layer and a battery pack housing when the vent assembly is installed on a battery pack. Accordingly, the failure layer may be positioned between the first adhesive layer and the second adhesive layer. For the avoidance of doubt, the vent stack defines an aperture that runs through the vent stack to expose the membrane of the vent assembly and the failure layer does not extend into or occlude the aperture of the vent stack.

[0026] In embodiments comprising a failure layer, the vent stack may be configured to fail at the interface between the failure layer and the adhesive layer. In embodiments where the vent stack comprises a first adhesive layer and a second adhesive layer, the vent stack may be configured to fail during use at the interface between the failure layer and the first adhesive layer. The vent stack may be configured to fail during use at the interface between the failure layer and the second adhesive layer.

[0027] The failure layer may comprise a material that adheres weakly to the adhesive layer. In embodiments where the vent stack comprises a first adhesive layer and a second adhesive layer the failure layer may adhere weakly to the first adhesive layer. The failure layer may adhere weakly to the second adhesive layer. The failure layer may comprise a first side that adheres weakly to the adhesive layer, the first adhesive layer or the second adhesive layer. The failure layer may comprise a second side opposed to the first side that adheres strongly to the adhesive layer, the first adhesive layer or the second adhesive layer.

[0028] The failure layer may comprise an adhesive (“failure layer adhesive”) that has weaker adhesion than the adhesive layer. Accordingly, when the pressure differential across the vent assembly is greater than the threshold pressure the failure layer will detach before the adhesive layer or the first adhesive layer and second adhesive layer. The failure layer may have a lower peel force than the adhesive layer. The failure layer may comprise a different adhesive than the adhesive layer. The failure layer may comprise a different amount of adhesive than the adhesive layer. The failure layer may have a different height or thickness of the failure layer adhesive than the adhesive layer. The failure layer may have a lower inplane thickness than the adhesive layer.

[0029] The failure layer may comprise a break material that is configured to break when the pressure differential across the vent assembly is greater than the threshold pressure. The break material may have a fibrillated microstructure. For example, the break material may comprise a material selected from the group ePTFE, ePE, or PTMPS. The break material may comprise an electrospun material. The break material may comprise an electrospun polyamide, polyurethane or polyimide, or a copolymer thereof. Accordingly, the vent stack may be configured to fail within the material of the failure layer rather than the interface between the failure layer and another component of the vent stack. The break material may have a low strength, typically a low z-strength. The break material is typically a layer that extends in the x / y plane. When a force is applied to the break material in the z-direction (the direction normal to the x / y plane of the layer) the break material breaks or fails. Typically, the break material breaks or fails when a force is applied in the z-direction away from break material (i.e. the break material is pulled in the z-direction rather than compressed). The break material may have a z-strength of 250 kPa or less. Accordingly, the break material may break or fail when a pressure of 250 kPa or less is applied to the break material in the z-direction. The z-strength of the break material may be measured using the test method as provided below. The break material may have a z-strength of less than 200 kPa. The break material may have a z-strength of less than 150 kPa. The break material may have a z-strength of from 10 kPa to 250 kPa. The break material may have a z-strength of from 10 kPa to 200 kPa. The break material may have a z-strength of from 10 kPa to 150 kPa. The break material may have a z-strength of from 10 kPa to 100 kPa. The break material may have a z-strength of from 10 kPa to 80 kPa. The break material may have a z-strength of from 20 kPa to 250 kPa. The break material may have a z-strength of from 30 kPa to 250 kPa. The break material may have a z-strength of from 40 kPa to 250 kPa. For example, the break material may have a z-strength of from 30 to 100 kPa, or the break material may have a z-strength of from 45 to 80 kPa.

[0030] Typically, in embodiments comprising a failure layer, the failure layer is the weak point of the vent stack. Accordingly, when the vent assembly is installed over an aperture in a housing and the threshold pressure is exceeded the structure of the vent stack is broken or disrupted at or within the failure layer such that a new aperture or opening is formed in the vent stack to thereby allow gas to escape through the aperture or opening from within a housing. In this way, the failure layer is configured to fail to thereby form the aperture or opening in the vent stack when the threshold pressure is exceeded. In embodiments where the failure layer comprises a break material, the failure layer is configured to fail by the breaking of the break material of the failure layer when the threshold pressure is exceeded forming the aperture or opening in the structure of the vent stack. In embodiments where the failure layer comprises a failure layer adhesive that has weaker adhesion than the adhesive layer, the failure layer is configured to fail by the failure layer adhesive that has weaker adhesion than the adhesive layer at least partially detaching to thereby form the aperture or opening in the vent stack. The vent stack may comprise a first adhesive layer positioned between the membrane and the failure layer and a second adhesive layer positioned on the side of the failure layer opposed to the side of the failure layer facing the membrane.

[0031] The membrane may be configured to prevent the passage of liquid water through the vent assembly. Accordingly, the membrane may prevent the ingress of liquid water into a battery pack upon which the vent assembly is installed during use. The membrane may comprise a material that is hydrophobic. The membrane may comprise a coating that is hydrophobic. The membrane may comprise a treatment that is hydrophobic. The membrane may comprise a coating that is oleophobic. The membrane may comprise of a treatment that is oleophobic.

[0032] The membrane may comprise a fluoropolymer. The fluoropolymer may comprise polytetrafluoroethylene (PTFE), polyvinlidene fluoride (PVDF), or fluorinated ethylene propylene (FEP) or combinations thereof. The membrane may comprise a non-fluoropolymer. The membrane may comprise polyparaxylylene (PPX), polyethylene (PE), poly(tetramethyl-p- silphenylenesiloxane) (PTMPS), polyamide 6, polyurethane, thermoplastic polyurethane, polypropylene, polyimide, or polyacrylonitrile (PAN) or combinations thereof.

[0033] Accordingly, the membrane may comprise PTFE, PPX, PE, PTMPS, polyamide 6, polyurethane, thermoplastic polyurethane, PVDF, FEP, polypropylene, polyimide, or PAN or combinations thereof. The membrane may comprise PTFE, PE, polyamide 6, or polyurethane or combinations thereof.

[0034] The membrane may be porous. The membrane may have a node and fibril microstructure. The material of the membrane may be fibrillated. The membrane may have a fibrillated microstructure.

[0035] The membrane may have an airflow across the membrane of at least 10 ml / h per cm2at 7 kPa. The airflow is measured using the test method defined herein. The membrane may have an airflow across the membrane of at least 20 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 30 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 40 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 50 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 75 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 100 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 10 ml / h per cm2at 7 kPa to 50000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 10 ml / h per cm2at 7 kPa to 50000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 30 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 40 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 50 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 75 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 100 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa.

[0036] Alternatively, the membrane may have substantially no airflow across the membrane at 7 kPa. Accordingly, the vent assembly may prevent the passage of gas across the vent assembly until the pressure differential across the vent assembly exceeds the threshold pressure. When the pressure threshold is exceeded the vent stack fails to thereby form an aperture or opening through which gas may pass to allow the pressure within a housing upon which the vent assembly is installed to be equalised.

[0037] The vent may further comprise a protective element positioned over the membrane. The protective element may be configured to protect the membrane from particulates and / or liquid water. The protective element may comprise a mesh, a scrim, ora captive ring. The protective element may comprise a protective housing that extends over the membrane. The protective element may be configured to form a barrier between the membrane and external contaminants. The protective element may be spaced apart from the membrane of the vent assembly to allow the membrane to be displaced toward the protective element during a failure event when the threshold pressure is exceeded.

[0038] The vent assembly may comprise a support positioned under the membrane. The support may span the aperture defined by the vent stack. The support typically has an airflow across the support that is at least the airflow across the membrane such that the airflow across the vent assembly is defined or limited by the membrane and not by the support. The support may provide structural support to the membrane to increase the resistance of the membrane to external forces. For example, the support may be a baffle or perforated element.

[0039] The adhesive layer may comprise a first portion and a second portion, wherein the first portion has strong adhesion and the second portion has weak adhesion such that during use the second portion is configured to fail when the pressure differential across the vent assembly is greater than the threshold pressure. The first portion may act as a hinge when the pressure differential across the vent assembly is greater than the threshold pressure such that the vent assembly or a portion of the vent assembly may pivot about the first portion.

[0040] The vent assembly may have a thickness of less than or equal to 2.0 mm. Accordingly, the vent assembly may extend from a housing less than 2.0 mm when the vent assembly is installed over an aperture of a housing. The vent assembly may have a thickness of less than 1 .5 mm. The vent assembly may have a thickness of less than 1 .0 mm. The vent assembly may have a thickness of 0.5 mm to 2.0 mm. The vent assembly may have a thickness of 0.5 mm to 1 .5 mm. The vent assembly may have a thickness of 0.5 mm to 1.0 mm. Accordingly, the vent assembly may be described as having a low profile.

[0041] In a second aspect there is provided a vent assembly comprising a membrane and a vent stack, the vent stack comprising an adhesive layer, wherein the vent stack is configured to fail during use when the temperature is greater than a threshold temperature.

[0042] The threshold temperature may be at least 90°C. The threshold temperature may be at least 100°C. The threshold temperature may be at least 120°C. The threshold temperature may be at least 150°C. The threshold temperature may be at least 200°C. The threshold temperature may be between 90°C and 300° C. The threshold temperature maybe between 100°C and 300° C. The threshold temperature may be between 120°C and 300° C. The threshold temperature maybe between 150°C and 300° C. The threshold temperature may be between 200°C and 300° C.

[0043] The adhesive layer may be configured to fail during use when the temperature is greater than the threshold temperature. An increase in temperature of the adhesive layer may reduce the viscosity of the adhesive of the adhesive layer. When the temperature is greater than the threshold temperature the viscosity of the adhesive of the adhesive layer may be reduced sufficiently such that the adhesive layer fails. An increase in temperature of the adhesive layer may reduce the adhesion of the adhesive layer. When the temperature is greater than the threshold temperature the adhesion of the adhesive layer may be reduced sufficiently such that the adhesive layer fails.

[0044] The vent stack may comprise a melt layer configured to melt or at least soften when the temperature is greater than the threshold temperature. Accordingly, the melt layer may comprise a material that has a melting point that is the threshold temperature. The melt layer may comprise a material selected from the group: polyethylene, polypropylene, polystyrene or co-polymers thereof.

[0045] The membrane may be configured to prevent the passage of liquid water through the vent assembly. Accordingly, the membrane may prevent the ingress of liquid water into a battery pack upon which the vent assembly is installed during use. The membrane may comprise a material that is hydrophobic. The membrane may comprise a coating that is hydrophobic.

[0046] The membrane may comprise a fluoropolymer. The fluoropolymer may comprise polytetrafluoroethylene (PTFE), polyvinlidene fluoride (PVDF), or fluorinated ethylene propylene (FEP) or combinations thereof. The membrane may comprise a non-fluoropolymer. The membrane may comprise polyparaxylylene (PPX), polyethylene (PE), poly(tetramethyl-p- silphenylenesiloxane) (PTMPS), polyamide 6, polyurethane, thermoplastic polyurethane, polypropylene, polyimide, or polyacrylonitrile (PAN) or combinations thereof.

[0047] Accordingly, the membrane may comprise PTFE, PPX, PE, PTMPS, polyamide 6, polyurethane, thermoplastic polyurethane, PVDF, FEP, polypropylene, polyimide, or PAN or combinations thereof. The membrane may comprise PTFE, PE, polyamide 6, or polyurethane or combinations thereof.

[0048] The membrane may be porous. The membrane may have a node and fibril microstructure. The material of the membrane may be fibrillated.

[0049] The membrane may have an airflow across the membrane of at least 10 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 20 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 30 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 40 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 50 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 75 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of at least 100 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 10 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 10 ml / h per cm2at 20 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 30 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 40 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 50 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 75 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa. The membrane may have an airflow across the membrane of from 100 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa.

[0050] The vent assembly may further comprise a protective element positioned over the membrane. The protective element may be configured to protect the membrane from particulates and / or liquid water. The protective element may comprise a mesh, a scrim, or a captive ring. The protective element may be configured to form a barrier between the membrane and external contaminants.

[0051] According to a third aspect a battery pack comprises a battery pack housing, a plurality of battery cells retained within the battery pack housing and a vent assembly, the battery pack housing defining an evacuation aperture and the vent assembly positioned across the evacuation aperture to thereby occlude the evacuation aperture, wherein the vent assembly comprises a membrane and vent stack, the vent stack comprises an adhesive layer, the vent stack being configured to fail during use when the pressure differential across the vent assembly is greater than a threshold pressure.

[0052] The threshold pressure may be at least 5 kPa. The threshold pressure may be at least 7 kPa. The threshold pressure may be at least 10 kPa. The threshold pressure may be at least 15 kPa. The threshold pressure may be at least 20 kPa.

[0053] The threshold pressure may be from 5 kPa to 300 kPa. The threshold pressure may be from 7 kPa to 300 kPa. The threshold pressure may be from 10 kPa to 300 kPa. The threshold pressure may be from 15 kPa to 300 kPa. The threshold pressure may be from 20 kPa to 300 kPa. The threshold pressure may be from 5 kPa to 250 kPa. The threshold pressure may be from 5 kPa to 200 kPa. The threshold pressure may be from 5 kPa to 150 kPa. The threshold pressure may be from 5 kPa to 100 kPa.

[0054] The vent stack may be configured to fail during use when the pressure within the battery pack housing is greater than 150 kPa. The vent stack may be configured to fail during use when the pressure within the battery pack housing is greater than 175 kPa. The vent stack may be configured to fail during use when the pressure within the battery pack housing is greater than 200 kPa.

[0055] Typically, the vent assembly is a vent assembly of the first aspect. The battery pack may further comprise a reinforcing element positioned over the vent assembly to thereby reinforce the vent assembly. The reinforcing element may be positioned spaced apart from the membrane of the vent assembly such that the membrane may be displaced when the vent stack fails.

[0056] The battery housing may comprise a vent recess around evacuation aperture and the vent assembly may be positioned within the vent recess. The vent recess may be configured to lower the vent assembly such that it is below the profile of the battery housing. Accordingly, the vent recess may protect the vent assembly from physical impacts to prevent accidental failure of the vent assembly.

[0057] The reinforcing element may be positioned over the vent recess.

[0058] In a fourth aspect there is provided a battery pack comprising a battery pack housing, a plurality of battery cells retained within the battery pack housing and a vent assembly, the battery pack housing defining an evacuation aperture and the vent assembly positioned across the evacuation aperture to thereby occlude the evacuation aperture, wherein the vent assembly comprises a membrane and vent stack, the vent stack comprises an adhesive layer, the vent stack being configured to fail during use when the temperature is greater than a threshold temperature.

[0059] The threshold temperature may be at least 90°C. The threshold temperature may be at least 100°C. The threshold temperature may be at least 120°C. The threshold temperature may be at least 150°C. The threshold temperature may be at least 200°C. The threshold temperature may be between 90°C and 300°C. The threshold temperature maybe between 100°C and 300°C. The threshold temperature may be between 120°C and 300°C. The threshold temperature maybe between 150°C and 300°C. The threshold temperature may be between 200°C and 300°C.

[0060] Typically, the vent assembly is a vent assembly of the second aspect.

[0061] The battery pack may further comprise a reinforcing element positioned over the vent assembly to thereby reinforce the vent assembly.

[0062] The battery housing may comprise a vent recess around evacuation aperture and the vent assembly is positioned within the vent recess. According to a fifth aspect there is provided an array of vent assemblies comprising a liner sheet and a plurality of vent assemblies according to the first aspect provided on the liner sheet. The liner sheet may comprise a slit or split under at least a portion of each vent assembly of the plurality of vent assemblies. The slit or split in the liner sheet may allow each vent assembly of the plurality of vent assemblies to be removed from the liner sheet more readily without damaging or causing the vent stack of each vent assembly to fail before the vent assembly is installed on a housing.

[0063] Each vent assembly of the plurality of vent assemblies may comprise a base adhesive layer that adheres the vent assembly to the liner sheet. The base adhesive layer may be thicker than the adhesive layer or each adhesive layer within the vent stack. The base adhesive layer may be stiffer than the adhesive layer or each adhesive layer within the vent stack. The base adhesive layer may allow each vent assembly to be removed from the liner sheet to be installed on a housing with a reduced risk of damage to the vent stack. For example, in embodiments where the vent stack comprises a failure layer, the base adhesive layer may allow each vent assembly by removed from the liner sheet to be installed on a housing with a reduced risk of premature failure of the failure layer.

[0064] In a sixth aspect a battery cell comprises a battery cell housing and a vent assembly, the battery cell housing defining an evacuation aperture and the vent assembly positioned across the evacuation aperture to thereby occlude the evacuation aperture, wherein the vent assembly comprises a membrane and vent stack, the vent stack comprises an adhesive layer, the vent stack being configured to fail during use when the pressure differential across the vent assembly is greater than a threshold pressure.

[0065] The vent assembly may be a vent assembly of the first aspect. Therefore, preferred and optional features of the vent assembly of the first aspect are preferred and optional features of the vent assembly of the present aspect.

[0066] Brief Description of the Figures

[0067] Embodiments of the present invention will now be described, by way of non-limiting example, with reference to the accompanying drawings.

[0068] Figure 1 : A bottom up schematic view of a vent assembly according to an embodiment;

[0069] Figure 2: A side schematic view of the vent assembly of Figure 1 installed over an aperture in a battery pack housing; Figure 3: A schematic side cross-section of a battery pack according to an embodiment with the vent assembly of Figures 1 and 2;

[0070] Figure 4: A bottom up schematic view of a vent assembly according to an embodiment;

[0071] Figure 5: A side schematic view of the vent assembly of Figure 4 installed over an aperture in a battery pack housing;

[0072] Figure 6: A schematic side cross-section of a battery pack according to an embodiment with the vent assembly of Figures 4 and 5;

[0073] Figure 7: A bottom up schematic view of a vent assembly according to an embodiment;

[0074] Figure 8: A side schematic view of the vent assembly of Figure 7 installed over an aperture in a battery pack housing;

[0075] Figure 9: A schematic side cross-section of a battery pack according to an embodiment with the vent assembly of Figures 7 and 8;

[0076] Figure 10: A schematic side cross-section of a vent assembly on a liner according to an embodiment;

[0077] Figure 11 : A top down view of a sheet of vent assemblies according to an embodiment; and Figure 12: A schematic side view of a vent assembly comprising a break layer according to an embodiment before and after the application of a force in z-direction.

[0078] Detailed Description

[0079] While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

[0080] To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as "a", "an" and "the" are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

[0081] Test Methods

[0082] Failure test

[0083] Samples are adhered to a test plate and allowed to sit for 24 hours for the adhesive to develop full strength. Test plates are fixed at the end of a tube inside a temperature chamber. Air pressure is ramped at fixed rates, and the pressure at which the vent failed is recorded. A slow ramp rate (“LFP-Slow”) increased the pressure by 0.08 bar per second. A fast ramp rate (“LFP-Fast”) increased the pressure by 1 bar per second.

[0084] Airflow

[0085] Airflow can be measured using an ATEQ D520 flow meter sourced from ATEQ, Livonia Ml, USA or equivalent. A test material is clamped over a 1 cm2opening, a pressure of 70mbar (7kPa) is applied, and airflow across the test material is measured.

[0086] Peel strength test

[0087] Peel strength is measured by conducting a 180deg peel from a test material and determining the force applied at which the peel occurred.

[0088] Z-strength Test

[0089] The cohesive strength of samples was measured under ambient conditions using a TAPPI- 541 (Zwick, Germany) device. A 75mm x 130mm piece of two-sided adhesive tape, such as 9500PC (3M Corporation), was attached to similar sized face of the bottom platen. A sample was placed over the tape covered bottom platen. The sample in between each of the five 25.4mm x 25.4mm test areas was slit with a scalpel to isolate the test samples. The upper platen, which has five identical 25.4mm x 25.4mm test areas, was covered with the same two sided adhesive tape. The upper & bottom platens were mounted in an Instron tensile testing machine with the two platens aligned at a 90 degree angle to each other. The platens with the sample in between were compressed together to 756 N at a rate of 12.7mm / min and held under that force for 30 seconds. The compressive force was then reduced to zero at a rate of 12.0kN / min. After 7.5 seconds of force removal, the platens were separated at the rate of 500 mm / min and the maximum force, in Newtons, to separate the platen was recorded. If the failure is cohesive in nature, the failed sample would be covering the surfaces of both the platens. If the cohesive strength of the sample is greater than the adhesive strength of the tape to the platens or of the tape to the sample, both the platens will not be covered with failed portion of both the samples. Samples in each of the 5 test areas were measured as above and Favg, the average of five maximum force values, is calculated.

[0090] The Z-strength of the sample in kPa = ((Favgin Newton) x 1000) / (645.16 mm2).

[0091] In the above procedure, care must be taken to ensure that the adhesive tape adheres only to the top and bottom surfaces of the porous test sample. The adhesive from the adhesive tape should not penetrate into the cross-section of the sample under the bonding pressure, as that can alter the Z-strength measurement. This can be checked by obtaining a SEM (scanning electron microscope) image of the sample cross-section after adhesive attachment. If adhesive infiltration into the sample is observed, the 756 N bonding force needs to be reduced until no infiltration occurs. Such adjustment of the bonding force is most likely necessary for samples with low areal mass.

[0092] Example 1

[0093] With reference to Figures 1 to 3, a vent assembly 1 comprises an adhesive layer 2 (acting as a vent stack) and a membrane 4. The membrane 4 comprises expanded polytetrafluoroethylene (ePTFE) (for example as disclosed in US patent US3953566 to Gore). The adhesive layer 2 extends around the perimeter of the membrane and defines an aperture 6. The adhesive layer 2 comprises a PET carrier with 50 pm silicone adhesive on either side of a 50 pm PET substrate and a substantially triangular notch 8 (acting as a discontinuity) that has a reduced width of adhesive and a failure point at the minimum width of the adhesive.

[0094] A battery pack 10 comprises a battery pack housing 12 and a plurality of prismatic can battery cells (for example, battery cell 14) retained therein. An aperture 16 is defined in the battery pack housing 12. The vent assembly 1 is installed over the aperture 16 such that the adhesive layer 2 extends around the aperture 16 to contact the battery pack housing 12 around the aperture 16 to thereby adhere the vent assembly 1 to the battery pack housing 12.

[0095] During use, the vent assembly 1 allows the passage of gas into and out of the battery pack housing 12 through the aperture 16 to thereby equalise the pressure within the battery pack housing 12. The membrane 4 of the vent assembly 1 also prevents the ingress of liquid water and particulates into the battery pack housing 12.

[0096] In the event of a battery cell failure or a thermal runaway event within the battery pack 10, a large volume of gas is typically produced that is generated at a rate that is greater than the rate at which gas can pass through the membrane 4 of the vent assembly 1 to thereby increase the pressure within the battery pack 10. If the pressure across the vent assembly 1 exceeds a threshold pressure, the adhesive layer 2 fails at the interface between the adhesive layer 2 and the membrane 4 over the notch 8 to thereby release the built-up pressure from within the battery pack housing 12.

[0097] Example 2

[0098] With reference to Figures 4 to 6 a vent assembly 20 comprises a vent stack 22 and a membrane 24 comprising expanded polyethylene (ePE). Expanded polyethylene (ePE) membranes may be produced by the following method. A ultra-high molecular weight polyethylene (LIHMWPE) resin having a molecular weight of approximately 7.6 million g / mol was obtained. A tape was prepared by the methods according to US patent 9,926,416 to Sbriglia et al. which is incorporated herein by reference in its entirety to produce a tape having a thickness of 0.14 mm. The tape was preheated at 135 °C for 30 seconds and then expanded in the machine direction at an expansion ratio of 1.5:1 at 150% per second and in the transverse direction at an expansion ratio of 2:1 at 300% per second to produce a membrane. The membrane was preheated at 160°C for 15 seconds and then expanded in the machine direction at a ratio of 4.5:1 at 0.7% per second and in the transverse direction at an expansion ratio of 8:1 at 1.4 % per second.

[0099] The vent stack 22 comprises a first adhesive layer 26, a failure layer 28 and a second adhesive layer 30. The first adhesive layer 26 adheres the failure layer 28 to the membrane 24. The second adhesive layer 30 adheres the failure layer 28 to a housing wall.

[0100] The first adhesive layer 26, and the second adhesive layer 30 comprise an acrylic adhesive provided on both sides of a PET substrate such as HPA TM 9392 as sourced from Avery Dennison. The failure layer 28 comprises a substrate comprising polyester with a first surface coated with fluorosilicone such as Scotchpak TM release liner 9709 from 3M, that has lower adhesion to the first adhesive layer 26.

[0101] An aperture 34 through the vent stack 22 is defined by the first adhesive layer 26, the failure layer 28 and the second adhesive layer 30 such that gas may pass through the vent stack 22 to the membrane 24.

[0102] A battery pack 36 comprises a battery pack housing 38 and a plurality of prismatic can battery cells (for example battery cell 40) are retained within the battery pack housing 38. An evacuation aperture 42 is defined in the battery pack housing 38 and the vent assembly 20 is installed over the evacuation aperture 42 such that the second adhesive layer 30 adheres the vent assembly 20 to the battery pack housing 38 around the evacuation aperture 42. The evacuation aperture 42 is provided in a recess 44 formed in a raised portion 46 of the battery pack housing 38 and a steel mesh 48 (acting as a protective element) is provided across the recess 44 and the vent assembly 20 installed therein to protect the vent assembly 20. The steel mesh 48 does not contact the vent assembly 20 such that in the event of failure of the vent stack 22 the membrane 24 of the vent assembly 20 is not held in place by the steel mesh 48. The provision of the vent assembly 20 within the recess 44 in the raised portion 46 of the battery pack housing 38 prevents the vent assembly 20 being physically contacted by exterior objects thereby preventing failure of the vent assembly 20 due to external contact.

[0103] During use the vent assembly 20 protects the evacuation aperture 42 from the ingress of liquid water or particulates whilst also allowing the passage of gas through the evacuation aperture 42 to thereby equalise the pressure within the battery pack housing 38 with the pressure of the external atmosphere.

[0104] In the event of a failure of one or more of the battery cells retained within the battery pack housing 38 gas may be generated at a rate that exceeds the rate at which gas can pass through the membrane 24 of the vent assembly 20. Accordingly, the pressure within the battery pack housing 38 increases. Once the pressure differential across the vent assembly 20 exceeds a threshold pressure the vent stack 22 fails at the interface between the first adhesive layer 26 and the failure layer 28. Accordingly, an opening is formed in the vent stack 22 to thereby allow gas to bypass the membrane 24 of the vent assembly 20 and to thereby flow out of the battery pack housing 38 at an increased rate, thereby releasing the pressure that has built up within the battery pack housing 38.

[0105] Example 3

[0106] With reference to Figures 7 to 9, a vent assembly 50 comprises a membrane 52 and a vent stack 54. The vent stack 54 comprises a first adhesive layer 56 a break layer 58 (acting as a failure layer) and a second adhesive layer 60. The membrane 52 comprises ePTFE (for example as disclosed in US patent US3953566 to Gore). The first adhesive layer 56 and the second adhesive layer 60 comprises a PET carrier with 50 pm silicone adhesive on either side of a 50 pm PET substrate. The break layer 58 comprises an ePTFE tape. The ePTFE tape was prepared using a fine powder PTFE blend as described in Example 1 of U.S. Patent 5,814,405 to Branca and formed into a porous article using the general methodology described in U.S. Patent 3,953,566 to Gore where an extruded, calendered and then dried tape is uniaxially expanded below its crystal melting point. The resulting article has a mass / area of 33 g / m2, a thickness of 378 micron, and a matrix tensile strength of 24,200 psi in the longitudinal direction and 240 psi in the transverse direction.

[0107] An aperture 62 is formed through the first adhesive layer 56, the break layer 58 and the second adhesive layer 60 such that gas may pass through the vent stack 54 to the membrane 52. The first adhesive layer 56 adheres the membrane 52 to the break layer 58. The second adhesive layer 60 adheres the break layer 58 and the vent assembly 50 to a substrate.

[0108] A battery pack 64 comprises a battery pack housing 66 and a plurality of prismatic can battery cells (for example battery cell 68) retained therein. The battery pack housing 66 comprises a recess 70 and defines an aperture 72 within the recess 70. The vent assembly 50 is installed within the recess 70 over the aperture 72 such that the second adhesive layer 60 adheres the vent assembly 50 to the battery pack housing 66 around the aperture 72. A cover 74 (acting as a protective element) extends across the recess 70 to cover the vent assembly 50 and protects the vent assembly 50 from accidental damage and physical trauma that may cause the vent assembly 50 to fail.

[0109] During use, the vent assembly 50 allows gas to pass between the interior of the battery pack housing 66 and the exterior of the battery pack housing 66 to thereby equalise the pressure of the battery pack 64. If a battery cell within the battery pack 64 fails or if there is a thermal runaway event, large volumes of gas are produced within the battery pack housing 66 at a rate that is greater than the rate at which gas can escape through the membrane 52 of the vent assembly 50. As a result the pressure within the battery pack housing 66 increases dramatically. As the pressure within the battery pack housing 66 increases the pressure differential across the vent assembly 50 increases. Once the pressure differential across the vent assembly 50 is greater than the threshold pressure, the force applied to the break layer 58 in the direction away from the battery pack housing 66 forms a break in the break layer 58 to thereby form an opening in the vent stack 50 to allow gas to bypass the membrane 52.

[0110] Each of the Examples 1 to 3 act as a pressure equalising vent during normal use whilst protecting the interior of the battery pack housing from liquid water and particulates. When the pressure within the battery pack housing is sufficiently high to result in the pressure differential to be greater than the threshold pressure, the vent stack of each example fails such that either an opening is formed within the vent stack or a portion of the vent assembly detaches from the battery pack housing to thereby open the aperture.

[0111] With reference to Figure 12, a vent assembly 120 comprises a membrane 122, a first adhesive layer 124, a break layer 126, and a second adhesive layer 128. The first adhesive layer 124, the break layer 126 and the second adhesive layer 128 form a vent stack 130. When the materials that make up the vent assembly are tested using the z-strength test described above, a tensile force 132 is applied in opposing z-directions. When this force produces a pressure across the surface area of the material that exceeds a threshold pressure, at least a portion of the material may break into a first portion 126a and a second portion 126b.

[0112] During use when the vent assembly 120 is installed over an aperture defined in a battery pack housing or a battery cell housing the internal pressure within the battery pack housing or battery cell housing is applied against the internal side of the membrane 122. This in turn applies a tensile force on the vent stack 130 across its cross section (tensile pressure). When this pressure applied to the vent stack 130 exceeds a threshold pressure, at least a portion of the break layer 126 within the vent stack 130 breaks into a first portion 126a and a second portion 126b.

[0113] Accordingly, the break layer 126 is the weak point in the vent assembly and is configured to structurally break to thereby form an aperture in the structure of the vent stack 130 of the vent assembly 120 to allow gas to escape through the aperture.

[0114] During use the vent assembly 120 is installed over an aperture in a battery housing (not shown). When the pressure inside the battery housing increases beyond an internal battery housing pressure, the pressure differential across the vent assembly 120 increases beyond the pressure threshold such that a pressure (force per area) is applied to the membrane 122 of the vent assembly. A force or pressure is thereby applied on the vent stack in the z-direction (i.e. applying a force on the membrane away from the battery housing) to thereby cause at least a portion of the break layer to break. As a result a new aperture is formed in the vent stack to thereby allow gas to escape from within the battery housing to rapidly reduce the pressure within the battery housing.

[0115] Specific Examples

[0116] Example vent assemblies were made comprising a membrane, two adhesive layers and a failure layer. The membrane was selected from membranes M1 to M5 as described below. The adhesive layer was selected from A1 to A3. The failure layer was selected from F1 to F9. An aperture is defined by the adhesive layer and the failure layer such that gas may pass through or from the membrane through the aperture. The failure layers F1 to F9 have a z- strength of less than 200 kPa and are shown to fail by fracturing or breaking when a differential pressure across the vent assembly exceeds a pressure threshold. Accordingly, the failure layers used in these examples are configured to fail when a pressure differential across the vent assembly exceeds a threshold pressure. Membrane

[0117] Membrane M1 is an expanded polytetrafluoroethylene (ePTFE) membrane made according to the teaching of US patent US 6,210,014 to Kubizne et al., which is incorporated herein by reference in its entirety and is commercially available under part numbers AVS9 / VE0020GMC, AVS120 / VE2122 and AVS113 / VE2114 from W. L. Gore & Associates, Inc.. The membrane further comprises an oleophobic treatment provided on the side of the membrane facing away from the vent stack in the vent assembly. The membrane had a minimum airflow of 7.8 L / (hour x cm2) at 70 mbar.

[0118] Membrane M2 is an expanded polyethylene (ePE) membrane obtained under part number Solupor® 14P02F from Gore Heerlen B.V. having a nominal airflow of 175 ml / (min x cm2) at 70mbar.

[0119] Membrane M3 is a multi-layer construction with an expanded PTFE layer thermally bonded to a polyester mesh screen. The outer side of the expanded PTFE layer includes an oleophobic treatment.

[0120] Membrane M4 is a multi-layer construction with a expanded PTFE layer thermally bonded to a non-woven polyester. M4 has minimum airflow of 6750 ml / (min x cm2) at 70mbar.

[0121] Membrane M5 is an expanded polytetrafluoroethylene (ePTFE) membrane made according to the teaching of US patent US 6,210,014 to Kubizne et al., which is incorporated herein by reference in its entirety. The membrane had a minimum airflow of 7.8 L / (hour x cm2) at 70 mbar.

[0122] Adhesive Layer

[0123] Adhesive layer A1 comprises a 38pm thick acrylic adhesive provided on both sides of a 50 pm polyethylene terephthalate (PET) substrate.

[0124] Adhesive layer A2 comprises a 10 pm thick acrylic adhesive provided on both sides of a 25 pm PET substrate.

[0125] Adhesive layer A3 comprises a 50 pm thick acrylic adhesive provided on both sides of a 100 pm PET substrate. Failure Layer

[0126] Failure layer F1 is an expanded PTFE material prepared using a fine powder PTFE blend as described in Example 1 of U.S. Patent 5,814,405 to Branca and formed into a porous article using the general methodology described in U.S. Patent 3,953,566 to Gore (which is incorporated herein by reference in its entirety) where an extruded, calendared and then dried tape is uniaxially expanded below its crystal melting point. The resulting article has a mass / area of 33 g / m2, a thickness of 378 micron, and a matrix tensile strength of 24,200 psi in the longitudinal direction and 240 psi in the transverse direction.

[0127] Failure layer F2 is an expanded polyethylene (ePE) membrane obtained from Gore Heerlen under part number 4P02A.

[0128] Failure layer F3 is an ePE membrane obtained from Gore Heerlen under part number 30M04A.

[0129] Failure layer F4 is an ePE membrane obtained from Gore Heerlen under part number 3P07A.

[0130] Failure layer F5 is an expanded polytetrafluoroethylene (ePTFE) membrane including particles of silica aerogel provided within the voids of the ePTFE membrane obtained from W. L. Gore & Associates, Inc. under part number 84002100.

[0131] Failure layer F6 is an ePTFE membrane including particles of silica aerogel provided within the voids of the ePTFE membrane obtained from W. L. Gore & Associates, Inc. under part number 84002250.

[0132] Failure layer F7 is a composite membrane comprising an ePTFE membrane including particles of graphite loaded into the voids between nodes and fibrils of the ePTFE membrane formed in the manner generally taught by US patent US 3,953,566 to Gore (which is incorporated herein by reference in its entirety) with PTFE resin being blended with graphite powder in proportion of four parts by weight resin to one part graphite.

[0133] Failure layer F8 is an electrospun polyamide (“Nylon 6”) made according to the teaching of patent US9101860B2 to Clarcor, Inc. (which is incorporated herein by reference in its entirety), with mass per unit area of 3.5 g / m2, thickness of 32.7 microns, and mean bubble point of 33 psi. Failure layer F9 is an electrospun polyurethane nanofiber membrane with the part number EKO-5 was obtained from Elmarco Ltd (Liberec, Czechia).

[0134] Table 1 : Z-strengths as measured using the method described above for the failure layers F1- F9.

[0135] For comparison, the membrane M5 was tested for the z-strength as per the failure layers above using the above test method and were found not to fail by the structure of the membrane breaking, but rather one of the adhesive layers connecting the membrane to the test equipment failed. Accordingly, the membranes do not correspond to failure layers.

[0136] Table 2: Examples 4 to 44 and average threshold pressures at which the vent stack fails at both a slow pressure ramp up (LFP-slow) and fast pressure ramp up (LFP-fast). As can be seen, the examples were found to fail in the structure of the failure layer when a threshold pressure for that vent assembly was exceeded. In other words, when the samples were reviewed after the sample has failed after the pressure has been ramped up, the material of the failure layer was observed to be present on both adjoining adhesive layers, therefore indicating that the material of the failure layer had fractured or broken rather than the adhesive layer either side of the failure layer detaching.

[0137] Example 45

[0138] With reference to Figures 10 and 11 , a sheet of vent assemblies 100 comprising a liner sheet 102 and an array of vent assemblies 104 (acting as a plurality of vent assemblies). Each vent assembly 106 of the array of vent assemblies 104 comprises a break layer 110 comprising a break material (acting as a failure layer), a breathable membrane 112 (acting as a membrane) and a first adhesive layer 114 between the breathable membrane 112 and the break layer 110. Each vent assembly 106 of the array of vent assemblies 104 further comprises a base adhesive layer 116 that is thicker than the first adhesive layer 114 positioned between the break layer 110 and the liner sheet 102. The liner sheet 102 comprises slits (for example 108) positioned under each vent assembly 106.

[0139] A vent assembly 106 is removed from the liner sheet 102 and the slit 108 in the liner sheet 102 facilitates the removal whilst minimizing the risk of damaging the break layer prior to installation of the vent assembly 106 over an aperture in a housing.

[0140] It will be understood by the skilled person that the feature of (1) sheet of vent assemblies may comprise the base adhesive layer that is thicker than the first adhesive layer and (2) the liner sheet comprising slits positioned under each vent assembly both facilitate the removal of a vent assembly from the liner sheet whilst minimising the risk of premature failure of the break material and can be provided in alternative embodiments alone (i.e. a sheet of vent assemblies having (1) or (2)) or in combination as described above.

[0141] While there has been hereinbefore described approved embodiments of the present invention, it will be readily apparent that many and various changes and modifications in form, design, structure and arrangement of parts may be made for other embodiments without departing from the invention and it will be understood that all such changes and modifications are contemplated as embodiments as a part of the present invention as defined in the appended claims.

[0142] Further embodiments and examples are defined in the following numbered clauses:

[0143] 1. A vent assembly comprising a membrane and a vent stack, the vent stack comprising an adhesive layer, wherein the vent stack is configured to fail during use when the pressure differential across the vent assembly when the vent assembly is installed across an aperture defined in a battery housing is greater than a threshold pressure, wherein the threshold pressure is at least 5 kPa.

[0144] 2. The vent assembly of clause 1 , wherein the threshold pressure is from 5 kPa to 300 kPa.

[0145] 3. The vent assembly of clause 1 or clause 2, wherein the adhesive layer is configured to fail.

[0146] 4. The vent assembly of clause 3, wherein the adhesive layer comprises an adhesive layer weak point and during use the adhesive layer is configured to fail at the weak point when the pressure differential across the vent assembly is greater than the threshold pressure.

[0147] 5. The vent assembly of clause 4, wherein the adhesive layer weak point corresponds to a discontinuity in the adhesive layer.

[0148] 6. The vent assembly of clause 5, wherein the adhesive layer extends around the perimeter of the membrane and has a width from the edge of the vent assembly towards the interior of the vent assembly and the discontinuity in the adhesive layer corresponds to a portion of the adhesive layer having a reduced width.

[0149] 7. The vent assembly of any preceding clause, wherein the vent stack further comprises a failure layer and the failure layer is configured to fail when the pressure differential across the vent assembly is greater than the threshold pressure.

[0150] 8. The vent assembly of clause 7, wherein the failure layer of the vent stack is positioned between the adhesive layer and the membrane.

[0151] 9. The vent assembly of clause 7 or clause 8, wherein the failure layer comprises an adhesive that has weaker adhesion than the adhesive layer.

[0152] 10. The vent assembly of any of clause 7 to clause 9, wherein the failure layer comprises a first major surface that weakly adheres to the adhesive layer.

[0153] 11. The vent assembly of any of clause 7 to clause 10, wherein the failure layer comprises a low strength material that is configured to break when the pressure differential across the vent assembly is greater than the threshold pressure.

[0154] 12. The vent assembly of any of clause 7 to clause 11 , wherein the vent stack comprises a first adhesive layer positioned between the membrane and the failure layer and a second adhesive layer positioned on the side of the failure layer opposed to the side of the failure layer facing the membrane.

[0155] 13. The vent assembly of any preceding clause, wherein the membrane is configured to prevent the passage of liquid water through the vent assembly.

[0156] 14. The vent assembly of any preceding clause, wherein the membrane has an airflow across the membrane of at least 10 ml / h per cm2at 50 kPa.

[0157] 15. The vent assembly of any preceding clause, wherein the membrane has an airflow across the membrane from 10 ml / h per cm2at 50 kPa to 200000 ml / h per cm2at 50 kPa. 16. The vent assembly of any preceding clause further comprising a protective element positioned over the membrane and the protective element is configured to protect the membrane from particulates and / or liquid water.

[0158] 17. The vent assembly of any preceding clause, wherein the adhesive layer comprises a first portion and a second portion, wherein the first portion has strong adhesion and the second portion has weak adhesion such that during use the second portion is configured to fail when the pressure differential across the vent assembly is greater than the threshold pressure.

[0159] 18. A vent assembly comprising a membrane and vent stack, the vent stack comprising an adhesive layer, wherein the vent stack is configured to fail during use when the temperature is greater than 90°C.

[0160] 19. The vent assembly according to clause 18, wherein the adhesive layer is configured to fail during use when the temperature is greater than 90°C.

[0161] 20. The vent assembly of clause 18 or clause 19, wherein the vent stack comprises a melt layer configured to melt or at least soften when the temperature is greater than 90°C.

[0162] 21 . A battery pack comprising a battery pack housing, a plurality of battery cells retained within the battery pack housing and a vent assembly, the battery pack housing defining an evacuation aperture and the vent assembly positioned across the evacuation aperture to thereby occlude the evacuation aperture, wherein the vent assembly comprises a membrane and a vent stack, the vent stack comprises an adhesive layer, the vent stack being configured to fail during use when the pressure differential across the vent assembly is greater than a threshold pressure.

[0163] 22. The battery pack of clause 21 , wherein the threshold pressure is at least 5 kPa.

[0164] 23. The battery pack of clause 21 or clause 22, wherein the threshold pressure is from 5 kPa to 150 kPa.

[0165] 24. The battery pack of any of clause 21 to clause 23, wherein the vent assembly is a vent assembly of any of clause 1 to clause 17.

[0166] 25. The battery pack of any of clause 21 to clause 24, wherein the battery pack further comprises a reinforcing element positioned over the vent assembly to thereby reinforce the vent assembly.

[0167] 26. The battery pack of any of clause 21 to clause 25, wherein the battery housing comprises a vent recess around evacuation aperture and the vent assembly is positioned within the vent recess.

[0168] 27. A battery pack comprising a battery pack housing, a plurality of battery cells retained within the battery pack housing and a vent assembly, the battery pack housing defining an evacuation aperture and the vent assembly positioned across the evacuation aperture to thereby occlude the evacuation aperture, wherein the vent assembly comprises a membrane and a vent stack, the vent stack comprises an adhesive layer, the vent stack being configured to fail during use when the temperature is greater than 90°C .

[0169] 28. The battery back of clause 27, wherein the vent assembly is a vent assembly of any of clause 18 to clause 20.

Claims

Claims1 . A vent assembly comprising a membrane and a vent stack, the vent stack comprising an adhesive layer and a failure layer, wherein the failure layer is configured to fail during use when the pressure differential across the vent assembly when the vent assembly is installed across an aperture defined in a battery housing is greater than a threshold pressure, wherein the threshold pressure is at least 5 kPa.

2. The vent assembly of claim 1 , wherein the threshold pressure is from 5 kPa to 300 kPa.

3. The vent assembly of claim 1 or claim 2, wherein the failure layer of the vent stack is positioned between the adhesive layer and the membrane.

4. The vent assembly of any preceding claim, wherein the failure layer comprises an adhesive that has weaker adhesion than the adhesive layer.

5. The vent assembly of any preceding claim, wherein the failure layer comprises a first major surface that weakly adheres to the adhesive layer.

6. The vent assembly of claim 4 or claim 5, wherein when the pressure differential across the vent assembly during use exceeds the threshold pressure the adhesive of the failure layer detaches to form an aperture or opening in the vent stack such that the failure layer fails.

7. The vent assembly of any of claim 1 to claim 3, wherein the failure layer comprises a low strength material that is configured to break when the pressure differential across the vent assembly is greater than the threshold pressure.

8. The vent assembly of claim 7, wherein the low strength material is a break material and when the pressure differential across the vent assembly during use exceeds the threshold pressure the break material breaks to form an aperture or opening in the vent stack such that the failure layer fails.

9. The vent assembly of claim 8, wherein the break material has a z-strength of less than 250 kPa.

10. The vent assembly of claim 8 or claim 9, wherein the break material has a z-strength of from 45 kPa to 80 kPa.

11. The vent assembly of any preceding claim, wherein the vent stack comprises a first adhesive layer positioned between the membrane and the failure layer and a second adhesive layer positioned on the side of the failure layer opposed to the side of the failure layer facing the membrane.

12. The vent assembly of any preceding claim, wherein the membrane is configured to prevent the passage of liquid water through the vent assembly.

13. The vent assembly of any preceding claim, wherein the membrane has an airflow across the membrane of at least 10 ml / h per cm2at 7 kPa.

14. The vent assembly of any preceding claim, wherein the membrane has an airflow across the membrane from 10 ml / h per cm2at 7 kPa to 800000 ml / h per cm2at 7 kPa.

15. The vent assembly of any of claim 1 to claim 12, wherein the membrane has substantially zero airflow across the membrane.

16. The vent assembly of any preceding claim further comprising a protective element positioned over the membrane and the protective element is configured to protect the membrane from particulates and / or liquid water.

17. A battery pack comprising a battery pack housing, a plurality of battery cells retained within the battery pack housing and a vent assembly according to any of claim 1 to claim 16, the battery pack housing defining an evacuation aperture and the vent assembly positioned across the evacuation aperture to thereby occlude the evacuation aperture.

18. The battery pack of claim 17, wherein the threshold pressure is at least 5 kPa.

19. The battery pack of claim 17 or claim 18, wherein the threshold pressure is from 5 kPa to 150 kPa.

20. The battery pack of any of claim 17 to claim 19, wherein the battery pack further comprises a reinforcing element positioned over the vent assembly to thereby reinforce the vent assembly.

21. The battery pack of any of claim 17 to claim 20, wherein the battery housing comprises a vent recess around evacuation aperture and the vent assembly is positioned within the vent recess.

22. A battery cell comprising a battery cell housing and a vent assembly of any of claim 1 to claim 16, the battery cell housing defining an evacuation aperture and the vent assembly positioned across the evacuation aperture to thereby occlude the evacuation aperture23. A sheet of vent assemblies comprising a liner sheet and a plurality of vent assemblies according to any of claim 1 to claim 16 provided on the liner sheet, the liner sheet comprises a slit or split under at least a portion of each vent assembly of the plurality of vent assemblies.

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