Battery housing and ventilation element

Abstract

A battery housing is provided comprising a housing wall comprising an impermeable substrate and at least one aperture disposed in the impermeable substrate, the or each aperture extending from a first side of the impermeable substrate to a second side of the impermeable substrate, and the maximum width of the or each hole is 0.1 [mu] m to 100 [mu] m, and wherein the ratio of the carbon dioxide (CO2) transmission rate to the water vapor (moisture) transmission rate of the housing wall is at least 2 using the test method described herein.

Description

Technical Field

[0001] The present disclosure relates to battery housings for batteries, and more particularly to battery housings that allow gases to escape from within the battery housing during use. Background Art

[0002] Batteries, such as lithium-ion batteries, are used to power a variety of electronic devices, including cars and mobile phones. Although battery performance has improved dramatically over the past few decades, some aspects of battery performance, such as battery life and battery output, still require improvement.

[0003] For example, a battery containing an electrolyte may release one or more gases during operation, and those gases may increase the pressure within the battery housing, thereby causing a rupture in the battery housing if not checked. It is therefore important that the gases be vented to reduce the internal pressure of the battery housing.

[0004] However, the vents or covers commonly used in the art to release gases generated by electrolyte decomposition also allow water vapor to enter the battery housing, negatively impacting the performance and life of the battery.

[0005] Therefore, there remains a need for an improved battery and an improved battery housing that allows for good release of gases released by the electrolyte and further minimizes water intrusion.

[0006] Thus, at least some embodiments described herein provide improved solutions for venting internal gases while minimizing water vapor intrusion into the battery housing. Summary of the Invention

[0007] According to a first aspect, a battery housing is provided, comprising a housing wall comprising an impermeable substrate and at least one aperture provided in the impermeable substrate, the aperture or each aperture extending from a first side of the impermeable substrate to a second side of the impermeable substrate, wherein the housing wall has a ratio of a carbon dioxide (CO2) transmission rate to a water vapor (moisture) transmission rate of at least 2 using the test method described herein.

[0008] The or each pore may have a maximum width of less than 100 μm. The or each pore may have a maximum width of less than 80 μm. The or each pore may have a maximum width of less than 60 μm. The or each pore may have a maximum width of less than 40 μm. The or each pore may have a maximum width of less than 20 μm.

[0009] The maximum width of the or each pore may be from 0.1 μm to 100 μm. The maximum width of the or each pore may be from 0.1 μm to 75 μm. The maximum width of the or each pore may be from 0.1 to 50 μm. The maximum width of the or each pore may be from 0.1 to 40 μm. The maximum width of the or each pore may be from 0.1 to 30 μm. The maximum width of the or each pore may be from 0.1 to 20 μm. The maximum width of the or each pore may be from 0.1 to 15 μm. The maximum width of the or each pore may be from 0.1 to 10 μm. The maximum width of the or each pore may be from 0.1 to 9 μm. The maximum width of the or each pore may be from 0.1 to 8 μm. The maximum width of the or each pore may be from 0.1 to 7 μm. The maximum width of the or each pore may be from 0.1 to 6 μm. The maximum width of the or each pore may be from 0.1 to 5 μm. The maximum width of the or each pore may be from 1 to 100 μm. The maximum width of the or each pore may be from 2 to 100 μm. The maximum width of the or each pore may be from 3 to 100 μm. The maximum width of the or each pore may be from 4 to 100 μm. The maximum width of the or each pore may be from 5 to 100 μm.

[0010] The or each pore may have an effective diameter of less than 100 μm. The or each pore may have an effective diameter of less than 80 μm. The or each pore may have an effective diameter of less than 60 μm. The or each pore may have an effective diameter of less than 40 μm. The or each pore may have an effective diameter of less than 20 μm.

[0011] The effective diameter of the or each pore may be from 0.1 μm to 100 μm. The effective diameter of the or each pore may be from 0.1 μm to 75 μm. The effective diameter of the or each pore may be from 0.1 to 50 μm. The effective diameter of the or each pore may be from 0.1 to 40 μm. The effective diameter of the or each pore may be from 0.1 to 30 μm. The effective diameter of the or each pore may be from 0.1 to 20 μm. The effective diameter of the or each pore may be from 0.1 to 15 μm. The effective diameter of the or each pore may be from 0.1 to 10 μm. The effective diameter of the or each pore may be from 0.1 to 9 μm. The effective diameter of the or each pore may be from 0.1 to 8 μm. The effective diameter of the or each pore may be from 0.1 to 7 μm. The effective diameter of the or each pore may be from 0.1 to 6 μm. The effective diameter of the or each pore may be from 0.1 to 5 μm. The or each pore may have an effective diameter of 1 to 100 μm. The or each pore may have an effective diameter of 2 to 100 μm. The or each pore may have an effective diameter of 3 to 100 μm. The or each pore may have an effective diameter of 4 to 100 μm. The or each pore may have an effective diameter of 5 to 100 μm.

[0012] As used herein, the term "effective diameter" refers to the diameter of the or each pore that would result from the measured cross-sectional area if the or each pore were approximately circular.

[0013] As used herein, the term "pore" refers to a pathway or channel that allows a fluid to pass from a first side of a substrate to a second side of the substrate. The pathway can be linear, allowing the fluid to pass through the substrate in a substantially straight line. As used herein, the term "pore" does not include pores that provide a tortuous pathway through a porous substrate, but rather a more direct pore.

[0014] The or each pore may form a direct path through the impermeable substrate. The or each pore may be formed in or through the impermeable substrate after the impermeable substrate has been formed. Thus, the or each pore is not, for example, a pore of a porous material.

[0015] The or each hole may have any cross-sectional shape. The or each hole may have a substantially circular or elliptical cross-section. The or each hole may have an angular cross-sectional shape with any number of sides, such as a triangle, rectangle (square or oblong), pentagon, hexagon, or octagon. The or each hole may have an irregular cross-sectional shape.

[0016] The or each hole may have a substantially cylindrical portion. The or each hole may be substantially cylindrical. Thus, the or each hole may have substantially the same maximum width and substantially the same cross-sectional area as the or each hole extends from the first side of the impermeable substrate to the second side of the impermeable substrate.

[0017] The or each hole may have a generally tapered portion. The or each hole may be generally tapered. Thus, the maximum width of the or each hole may increase or decrease as the or each hole extends from the first side to the second side.

[0018] The hole or holes may be formed in the impermeable substrate by any suitable method. The hole or holes may be formed by mechanical drilling. The hole or holes may be formed by laser drilling. In embodiments where the hole or holes are formed by laser drilling, the maximum width of the hole or holes may decrease slightly from the first side (where the laser is incident) to the second side due to the weakening of the laser through the impermeable substrate. Therefore, the hole or holes may have a first maximum width or effective diameter on the first side of the impermeable substrate, and the hole or holes may have a second maximum width or effective diameter on the second side of the impermeable substrate. The first maximum width or effective diameter may be greater than the second maximum width or effective diameter. The first maximum width or effective diameter may be less than the second maximum width or effective diameter.

[0019] The or each pore may be formed by piercing the impermeable substrate. The or each pore may be formed by piercing the impermeable substrate by pushing or forcing a piercing element through the impermeable substrate. The piercing element may be a needle, capillary tube, or the like.

[0020] In embodiments where more than one aperture is provided in the impermeable substrate, the more than one aperture may be formed by an array of piercing elements. The piercing elements may be arranged in a regular pattern such that the more than one aperture provided thereby in the impermeable substrate is arranged in a regular pattern.

[0021] The shell wall may include at least two holes disposed in the impermeable substrate. The shell wall may include at least three holes disposed in the impermeable substrate. The shell wall may include at least four holes disposed in the impermeable substrate. The shell wall may include at least five holes disposed in the impermeable substrate. The shell wall may include at least six holes disposed in the impermeable substrate. The shell wall may include at least seven holes disposed in the impermeable substrate. The shell wall may include at least eight holes disposed in the impermeable substrate. The shell wall may include at least nine holes disposed in the impermeable substrate. The shell wall may include at least ten holes disposed in the impermeable substrate.

[0022] The shell wall may comprise 1 to 100 pores disposed in the impermeable substrate. The shell wall may comprise 1 to 75 pores disposed in the impermeable substrate. The shell wall may comprise 1 to 50 pores disposed in the impermeable substrate. The shell wall may comprise 1 to 40 pores disposed in the impermeable substrate. The shell wall may comprise 1 to 30 pores disposed in the impermeable substrate. The shell wall may comprise 1 to 20 pores disposed in the impermeable substrate. The shell wall may comprise 1 to 15 pores disposed in the impermeable substrate. The shell wall may comprise 1 to 10 pores disposed in the impermeable substrate.

[0023] In some embodiments, the shell wall may include one hole disposed in the impermeable substrate. In some embodiments, the shell wall may include two holes disposed in the impermeable substrate. In some embodiments, the shell wall may include three holes disposed in the impermeable substrate. In some embodiments, the shell wall may include four holes disposed in the impermeable substrate. In some embodiments, the shell wall may include five holes disposed in the impermeable substrate.

[0024] As used herein, the "ratio of CO2 transmission rate to water vapor transmission rate" is calculated by dividing the CO2 transmission rate of the substrate by the water vapor transmission rate. The ratio of CO2 transmission rate to water vapor transmission rate is unitless (i.e., dimensionless). Thus, a ratio of at least 2 means that at a given pressure, at least twice the volume of CO2 as water vapor is transmitted through the housing wall.

[0025] Typically, the battery housing defines an enclosed space that can retain the electrolyte.

[0026] It is important to prevent the intrusion of water (in liquid or vapor form) into the interior of the battery housing, as the presence of water can significantly affect the efficiency and performance of the battery.

[0027] Furthermore, during the life of the battery, gases such as carbon dioxide (CO), hydrogen (H), carbon monoxide (CO), or methane (CH) may be produced as byproducts of electrochemical reactions within the battery housing. To ensure that the pressure within the battery housing remains within operating limits to avoid rupture of the housing wall, it is advantageous for the gases to be able to escape from the interior of the battery housing.

[0028] It has been unexpectedly discovered that the battery housing of the present invention is capable of minimizing water intrusion into the interior of the battery housing while at the same time allowing gases to escape.

[0029] The CO2 permeability through the housing wall may be at least 25 cm 3 / day. The CO2 permeability through the housing wall may be at least 50 cm3 / day. The CO2 permeability through the housing wall may be at least 75 cm 3 / day. The CO2 permeability through the housing wall may be at least 100 cm 3 / day. The CO2 permeability through the housing wall may be at least 150 cm 3 / day. The CO2 permeability through the housing wall may be at least 200 cm 3 / day. The CO2 permeability through the shell wall can be 25cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the shell wall can be 50cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the shell wall can be 75cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the shell wall can be 100cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the shell wall can be 150cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the shell wall can be 200cm 3 / day to 10,000cm 3 / day.

[0030] The CO2 permeability is usually measured at 37.8°C and 1 bar pressure to 5 cm 2 It is to be understood that when using the unit "cm 3 ”, it is the volume at standard temperature and pressure (defined herein as a temperature of 0° C. and a pressure of 1 bar).

[0031] The CO2 permeability through the housing wall may be at least 50,000 cm 3 / (m 2 ·day·bar), converted to standard temperature and pressure. The CO2 permeability through the housing wall may be at least 75,000 cm 3 / (m 2 The CO2 permeability through the housing wall may be at least 100,000 cm 3 / (m 2 The CO2 permeability through the housing wall may be at least 150,000 cm 3 / (m 2 The CO2 permeability through the housing wall may be at least 200,000 cm 3 / (m 2 ·day·bar). The CO2 permeability through the outer shell wall can be 25,000 cm 3 / (m 2 ·day·bar) to 10,000,000 cm 3 / (m 2 ·day·bar). The CO2 permeability through the outer shell wall can be 50,000 cm 3 / (m 2 ·day·bar) to 10,000,000 cm 3 / (m 2 ·day·bar). The CO2 permeability through the outer shell wall can be 75,000 cm 3 / (m 2 ·day·bar) to 10,000,000 cm 3 / (m 2 ·day·bar). The CO2 permeability through the outer shell wall can be 100,000 cm 3 / (m 2 ·day·bar) to 10,000,000 cm 3 / (m 2 ·day·bar). The CO2 permeability through the outer shell wall can be 150,000 cm<(day·bar) to 10,000,000 cm / (m 2 ·day·bar) to 10,000,000 cm 3 / (m 2 ·day·bar). The CO2 permeability through the outer shell wall can be 200,000 cm 3 / (m 2 ·day·bar) to 10,000,000 cm 3 / (m<(day·bar).·day·bar).

[0032] It will be understood that it is desirable for the water vapor permeability through the outer shell wall to be as low as possible. For example, the water vapor permeability through the outer shell wall can be less than 200,000 cm 3 / (m 2 ·day·bar). The water vapor permeability through the outer shell wall can be less than 150,000 cm 3 / (m 2 / / (m ·day·bar). The water vapor permeability through the outer shell wall can be less than 100,000 cm 3 / (m 2 ·day·bar). The water vapor permeability through the outer shell wall can be less than 75,000 cm 3 / (m 2 ·day·bar).

[0033] The ratio of the CO2 permeability to the water permeability of the outer shell wall is at least 3. The ratio of the CO2 permeability to the water permeability of the outer shell wall is at least 5. The ratio of the CO2 permeability to the water permeability of the outer shell wall is at least 10. The ratio of the CO2 permeability to the water permeability of the outer shell wall is at least 20. The ratio of the CO2 permeability to the water permeability of the outer shell wall is at least 30. It will be understood that it is desirable for this application for the ratio to be as high as possible in order to maximize the rate of CO2 transfer out of the battery enclosure through the outer shell wall while minimizing the rate of water ingress into the battery enclosure.

[0034] The ratio of the CO2 permeability to the water permeability of the outer shell wall can be from 2 to 1000. The ratio of the CO2 permeability to the water permeability of the outer shell wall can be from 3 to 1000. The ratio of the CO2 permeability to the water permeability of the outer shell wall can be from 5 to 1000. The ratio of the CO2 permeability to the water permeability of the outer shell wall can be from 10 to 1000. The ratio of the CO2 permeability to the water permeability of the outer shell wall can be from 20 to 1000. The ratio of the CO2 permeability to the water permeability of the outer shell wall can be from 30 to 1000. The ratio of the CO2 permeability to the water permeability of the outer shell wall can be from 50 to 1000.

[0035] The CO2 permeability described herein is the CO2 permeability measured at 37.8 °C using the method described below. The water or water vapor permeability described herein is the water or water vapor permeability measured at 37.8 °C using the method described below. The gas volume is converted from the measured temperature to the standard temperature and pressure described above.

[0036] As used herein, the term "non-permeable substrate" means that the substrate has a low water vapor permeability. As used herein, low water vapor (moisture) permeability is understood to mean a water vapor permeability of less than 5 g / (m 2 day) or 100,000 cm 3 / (m 2 ·day·bar) at 100% RH and 37.8 °C.

[0037] The non-permeable substrate can comprise a polymer. The polymer can be a fluoropolymer. The polymer can be a non-fluoropolymer. The polymer can be an expanded polymer. The polymer can be a densified expanded polymer.

[0038] For the avoidance of doubt, the term "densified expanded polymer film" refers to a polymer film that has been expanded below its melting temperature and subsequently densified. Therefore, it should be understood that the density of at least one layer of the densified expanded polymer film is greater than the density of the corresponding undensified expanded polymer film. Those skilled in the art will appreciate that a polymer film that has been expanded below its melting temperature and then densified can have a lower porosity than a corresponding polymer film of the same material that has been expanded but not densified. The densification step can close a certain proportion of the pores in the expanded polymer film. Therefore, the degree of densification of the expanded polymer film can allow for control of gas permeability through the film and tailor it to the desired application.

[0039] The polymer may be selected from polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), perfluoro(alkyl vinyl ether) ("PAVE", including perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), etc.), vinylidene fluoride (VDF), fluoroethylene propylene (FEP), chlorotrifluoroethylene (CTFE) or copolymers, or combinations thereof

[0040] The impermeable substrate may comprise a metal. For example, the impermeable substrate may comprise aluminum, iron, copper, tin, or an alloy, or a combination thereof.

[0041] The impermeable substrate may have a certain thickness between the first side and the second side. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 3. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 5. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 7. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 10. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 15. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 20. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 25. Therefore, the ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be at least 3, 5, 7, 10, 15, 20, 25, or a value therebetween.

[0042] The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 3 to 100. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 5 to 100. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 7 to 100. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 10 to 100. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 15 to 100. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 20 to 100. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 25 to 100. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 2 to 90. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 2 to 80. The ratio of the thickness of the non-permeable substrate to the maximum width of the or each pore may be from 2 to 70. The ratio of the thickness of the impermeable substrate to the maximum width of the or each pore may be from 2 to 60.

[0043] The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or each pore may be at least 0.1 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or each pore may be at least 0.5 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or each pore may be at least 0.6 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or each pore may be at least 0.7 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or each pore may be at least 0.8 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or each pore may be at least 0.9 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or each pore may be at least 1 / μm.

[0044] The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 0.1 to 1000 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 0.1 to 750 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 0.1 to 500 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 0.1 to 250 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 0.1 to 100 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 0.5 to 1000 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 1 to 1000 / μm. The ratio of the thickness of the non-permeable substrate to the cross-sectional area of the pore or pores may be from 2 to 1000 / μm.

[0045] The battery housing of the present invention may include at least one protective element disposed on at least one of the first and second sides of the impermeable substrate, and may cover the hole or holes. The at least one protective element may prevent particulate matter from entering the hole or holes. The at least one protective element may prevent liquid from entering the hole or holes. The battery housing may include two protective elements. The two protective elements may include a first protective element disposed on the first side and a second protective element disposed on the second side, such that the hole or holes are covered by both the first protective element and the second protective element. Thus, the first end of the hole or holes may be covered by the first protective element, while the second end of the hole or holes may be covered by the second protective element.

[0046] The at least one protective element may comprise an open material.

[0047] As used herein, the term "open-porous material" refers to a material having a high porosity and low resistance to gas flow therethrough. In the context of the present aspect, the CO2 transmission rate through the open-porous material is higher than the CO2 transmission rate through the housing wall, so that the CO2 transmission rate through the or each pore in the non-permeable substrate of the housing wall is not restricted.

[0048] The at least one protective element may comprise a highly porous material. The at least one protective element may comprise a material having a higher CO2 permeability than the housing wall. Thus, the CO2 permeability of the entire battery housing is not limited by the at least one protective element, but rather by the CO2 permeability of the housing wall. The CO2 permeability of the at least one protective element may be at least 200,000,000 cm 3 / (m 2 The at least one protective element may have a CO2 permeability of at least 300,000,000 cm 3 / (m 2 The at least one protective element may have a CO2 permeability of at least 400,000,000 cm 3 / (m 2 The at least one protective element may have a CO2 permeability of at least 500,000,000 cm 3 / (m 2 The at least one protective element may have a CO2 permeability of at least 600,000,000 cm 3 / (m 2 The at least one protective element may have a CO2 permeability of at least 700,000,000 cm 3 / (m2 The at least one protective element may have a CO2 permeability of at least 800,000,000 cm 3 / (m 2 The at least one protective element may have a CO2 permeability of at least 1,000,000,000 cm 3 / (m 2 The at least one protective element may have a CO2 permeability of about 200,000,000 cm 3 / (m 2 · Japan · Brazil) to about 50,000,000,000cm 3 / (m 2 The at least one protective element may have a CO2 permeability of about 300,000,000 cm 3 / (m 2 · Japan · Brazil) to about 50,000,000,000cm 3 / (m 2 The at least one protective element may have a CO2 permeability of about 400,000,000 cm 3 / (m 2 · Japan · Brazil) to about 50,000,000,000cm 3 / (m 2 The at least one protective element may have a CO2 permeability of about 500,000,000 cm 3 / (m 2 · Japan · Brazil) to about 50,000,000,000cm 3 / (m 2 The at least one protective element may have a CO2 permeability of about 600,000,000 cm 3 / (m 2 · Japan · Brazil) to about 50,000,000,000cm 3 / (m 2 The at least one protective element may have a CO2 permeability of about 700,000,000 cm 3 / (m 2 · Japan · Brazil) to about 50,000,000,000cm 3 / (m 2 The at least one protective element may have a CO2 permeability of about 800,000,000 cm 3 / (m 2 · Japan · Brazil) to about 50,000,000,000cm 3 / (m 2·Day·Brazil).

[0049] The at least one protective element may comprise an expanded polymer. The at least one protective element may comprise expanded polytetrafluoroethylene or expanded polyethylene. The at least one protective element may comprise an expanded polymer having a fibrillated microstructure.

[0050] The at least one protective element may comprise a coating. The coating may be oleophobic. The coating may hinder or disrupt the passage of solvents or electrolytes through the hole or holes from within the battery enclosure. The coating may hinder or disrupt the wetting of the non-permeable substrate.

[0051] The thickness of the at least one protective element may be less than 200 μm. The thickness of the at least one protective element may be less than 150 μm. The thickness of the at least one protective element may be less than 100 μm. The thickness of the at least one protective element may be less than 50 μm. The thickness of the at least one protective element may be less than 40 μm. The thickness of the at least one protective element may be less than 30 μm.

[0052] The thickness of the at least one protective element may be from 1 μm to 200 μm. The thickness of the at least one protective element may be from 1 μm to 150 μm. The thickness of the at least one protective element may be from 1 μm to 100 μm. The thickness of the at least one protective element may be from 1 μm to 50 μm. The thickness of the at least one protective element may be from 1 μm to 40 μm. The thickness of the at least one protective element may be from 1 μm to 30 μm.

[0053] In some embodiments, the enclosure wall may be rigid. Thus, the enclosure wall may be configured to withstand deformation that changes the shape of the enclosure wall. Alternatively, the enclosure wall may be flexible. Thus, the enclosure wall may be configured to deform at least partially so as to change the shape of the enclosure wall. For example, the enclosure wall may be a bladder-type enclosure wall and the battery enclosure may be a battery pouch.

[0054] In some embodiments, the housing may include at least one of a metal, a metal alloy, or a combination thereof. In some embodiments, the housing wall may include at least one of: iron (Fe), aluminum (Al), or alloys thereof. In some embodiments, the housing wall may include at least one polymer. The at least one polymer may include a fluorinated polymer such as PTFE, PFA, FEP, or a copolymer thereof. The at least one polymer may include a non-fluorinated polymer such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), or a copolymer thereof. The housing wall may include a combination of at least one metal layer and at least one polymer layer. The housing wall may include at least one metal layer disposed between at least two polymer layers. Thus, the housing wall may include at least one metal layer, wherein at least one polymer layer is disposed on a first side of the at least one metal layer and at least one polymer layer is disposed on a second side of the at least one metal layer. Thus, the at least one metal layer may be protected by the at least one polymer layer on the first side and protected by the at least one polymer layer on the second side. The at least one polymer layer on the first side may be the same as the at least one polymer layer on the second side. The at least one polymer layer on the first side may include the same polymer as the at least one polymer layer on the second side. The at least one polymer layer on the first side may be different from the at least one polymer layer on the second side.The at least one polymer layer on the first side may comprise a different polymer than the at least one polymer layer on the second side.

[0055] In embodiments where the housing wall comprises a plurality of layers, it will be appreciated that the or each aperture extends through each of the plurality of layers to form a through-hole through the housing wall.

[0056] In a second aspect, there is provided a ventilation element comprising an impermeable substrate comprising at least one pore, the or each pore extending from a first side of the impermeable substrate to a second side of the impermeable substrate.

[0057] The or each pore may have a maximum width of less than 100 μm. The or each pore may have a maximum width of less than 80 μm. The or each pore may have a maximum width of less than 60 μm. The or each pore may have a maximum width of less than 40 μm. The or each pore may have a maximum width of less than 20 μm.

[0058] The maximum width of the or each pore may be from 0.1 μm to 100 μm. The maximum width of the or each pore may be from 0.1 μm to 75 μm. The maximum width of the or each pore may be from 0.1 to 50 μm. The maximum width of the or each pore may be from 0.1 to 40 μm. The maximum width of the or each pore may be from 0.1 to 30 μm. The maximum width of the or each pore may be from 0.1 to 20 μm. The maximum width of the or each pore may be from 0.1 to 15 μm. The maximum width of the or each pore may be from 0.1 to 10 μm. The maximum width of the or each pore may be from 0.1 to 9 μm. The maximum width of the or each pore may be from 0.1 to 8 μm. The maximum width of the or each pore may be from 0.1 to 7 μm. The maximum width of the or each pore may be from 0.1 to 6 μm. The maximum width of the or each pore may be from 0.1 to 5 μm. The maximum width of the or each pore may be from 1 to 100 μm. The maximum width of the or each pore may be from 2 to 100 μm. The maximum width of the or each pore may be from 3 to 100 μm. The maximum width of the or each pore may be from 4 to 100 μm. The maximum width of the or each pore may be from 5 to 100 μm.

[0059] The or each pore may have an effective diameter of less than 100 μm. The or each pore may have an effective diameter of less than 80 μm. The or each pore may have an effective diameter of less than 60 μm. The or each pore may have an effective diameter of less than 40 μm. The or each pore may have an effective diameter of less than 20 μm.

[0060] The effective diameter of the or each pore may be from 0.1 μm to 100 μm. The effective diameter of the or each pore may be from 0.1 μm to 75 μm. The effective diameter of the or each pore may be from 0.1 to 50 μm. The effective diameter of the or each pore may be from 0.1 to 40 μm. The effective diameter of the or each pore may be from 0.1 to 30 μm. The effective diameter of the or each pore may be from 0.1 to 20 μm. The effective diameter of the or each pore may be from 0.1 to 15 μm. The effective diameter of the or each pore may be from 0.1 to 10 μm. The effective diameter of the or each pore may be from 0.1 to 9 μm. The effective diameter of the or each pore may be from 0.1 to 8 μm. The effective diameter of the or each pore may be from 0.1 to 7 μm. The effective diameter of the or each pore may be from 0.1 to 6 μm. The effective diameter of the or each pore may be from 0.1 to 5 μm. The or each pore may have an effective diameter of 1 to 100 μm. The or each pore may have an effective diameter of 2 to 100 μm. The or each pore may have an effective diameter of 3 to 100 μm. The or each pore may have an effective diameter of 4 to 100 μm. The or each pore may have an effective diameter of 5 to 100 μm.

[0061] The ventilation element of the present invention may comprise a first protective element. The first protective element may be positioned on a first side of the impermeable substrate and may block the hole or holes. The ventilation element of the present invention may comprise a second protective element. The second protective element may be positioned on a second side of the impermeable substrate and may block the hole or holes.

[0062] The first and second protective elements may comprise an expanded polymer selected from the group consisting of expanded polytetrafluoroethylene and expanded polyethylene.

[0063] Each of the first and second protective elements may have a CO2 permeability higher than the or each aperture.

[0064] The first and / or second protective element may comprise a coating. The coating may be oleophobic. The coating may hinder or disrupt the passage of solvents or electrolytes through the or each pore. The coating may hinder or disrupt wetting of the non-permeable substrate.

[0065] The ventilation element may comprise at least two holes disposed in the impermeable substrate. The ventilation element may comprise at least three holes disposed in the impermeable substrate. The ventilation element may comprise at least four holes disposed in the impermeable substrate. The ventilation element may comprise at least five holes disposed in the impermeable substrate. The ventilation element may comprise at least six holes disposed in the impermeable substrate. The ventilation element may comprise at least seven holes disposed in the impermeable substrate. The ventilation element may comprise at least eight holes disposed in the impermeable substrate. The ventilation element may comprise at least nine holes disposed in the impermeable substrate. The ventilation element may comprise at least ten holes disposed in the impermeable substrate.

[0066] The ventilation element may comprise 1 to 100 holes arranged in the impermeable substrate. The ventilation element may comprise 1 to 75 holes arranged in the impermeable substrate. The ventilation element may comprise 1 to 50 holes arranged in the impermeable substrate. The ventilation element may comprise 1 to 40 holes arranged in the impermeable substrate. The ventilation element may comprise 1 to 30 holes arranged in the impermeable substrate. The ventilation element may comprise 1 to 20 holes arranged in the impermeable substrate. The ventilation element may comprise 1 to 15 holes arranged in the impermeable substrate. The ventilation element may comprise 1 to 10 holes arranged in the impermeable substrate.

[0067] The impermeable substrate may comprise a polymer. The polymer may be a fluorinated polymer. The polymer may be a non-fluorinated polymer. The polymer may be an expanded polymer. The polymer may be a densified expanded polymer.

[0068] For the avoidance of doubt, the term "densified expanded polymer membrane" refers to the polymer membrane as defined in the first aspect.

[0069] The polymer may be selected from polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), perfluoro(alkyl vinyl ether) ("PAVE", including perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), etc.), vinylidene fluoride (VDF), fluoroethylene propylene (FEP), chlorotrifluoroethylene (CTFE) or copolymers, or combinations thereof

[0070] The impermeable substrate may comprise a metal. For example, the impermeable substrate may comprise aluminum, iron, copper, tin, or alloys thereof, or combinations thereof.

[0071] The ventilation elements of the present invention may have a ratio of carbon dioxide (CO2) transmission rate to water vapor (moisture) transmission rate of at least 2 using the test method described herein.

[0072] The CO2 transmission rate through the ventilation element may be at least 25 cm 3 / (day). The CO2 permeability through the ventilation element may be at least 50cm 3 / day. The CO2 permeability through the ventilation element may be at least 75 cm 3 / day. The CO2 permeability through the ventilation element may be at least 100 cm 3 / day. The CO2 permeability through the ventilation element may be at least 150 cm 3 / day. The CO2 permeability through the ventilation element may be at least 200 cm 3 / day. The CO2 permeability through the ventilation element can be 25cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the ventilation element can be 50cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the ventilation element can be 75cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the ventilation element can be 100cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the ventilation element can be 150cm 3 / day to 10,000cm 3 / day. The CO2 permeability through the ventilation element can be 200cm 3 / day to 10,000cm 3 / day.

[0073] It will be understood that it is desirable for the water vapor transmission rate through the ventilation element to be as low as possible. For example, the water vapor transmission rate through the ventilation element may be less than 200,000 cm 3 / (m 2 ·day·bar). The water vapor transmission rate through the ventilation element may be less than 150,000 cm 3 / (m 2 ·day·bar). The water vapor transmission rate through the ventilation element may be less than 100,000 cm 3 / (m 2 ·day·bar). The water vapor transmission rate through the ventilation element may be less than 75,000 cm 3 / (m 2 ·day·bar).

[0074] The ventilation element of the present invention may be configured to be installed within an electronic housing. The ventilation element may be configured to be installed within the housing wall of a battery housing. The non-permeable substrate of the ventilation element may be part of the non-permeable substrate of the housing wall. The non-permeable substrate of the ventilation element may be configured to be inserted into a pore in the non-permeable substrate of the housing wall.

[0075] Thus, the CO2 transmission rate throughout the ventilation element may not be limited by the first protective element or the second protective element, but rather by the CO2 transmission rate of the pore or pores of the non-permeable substrate.

[0076] To avoid doubt, the features of the non-permeable substrate in the first aspect are the features of the second aspect. Additionally, the features of at least one protective element in the first aspect are the features of the first and second protective elements in the second aspect.

[0077] According to a third aspect, there is provided a battery comprising the battery housing according to the first aspect.

[0078] The battery may be a secondary battery. The secondary battery may be a lithium-ion battery.

[0079] As used herein, the term "lithium-ion battery" refers to any battery in which lithium ions are configured to move between a negative electrode and a positive electrode during battery operation. Examples of lithium-ion batteries include, but are not limited to: lithium-ion polymer (LiPo) batteries, lithium-sulfur (Li-S) batteries, and thin-film lithium batteries.

[0080] The positive electrode may be selected from: lithium nickel manganese cobalt oxide (“NMC”), lithium nickel cobalt aluminum oxide (“NCA”), lithium manganese oxide (“LMO”), lithium iron phosphate (“LFP”), cobalt lithium oxide (“LCO”), or any combination thereof.

[0081] The negative electrode may be selected from the group consisting of lithium, graphite, lithium titanate ("LTO"), tin-cobalt alloy, or any combination thereof.

[0082] In some embodiments, the battery may include at least one separator. The at least one separator may include at least one material selected from the group consisting of polypropylene, polyethylene, at least one tetrafluoroethylene (TFE) polymer or copolymer, at least one homopolymer of vinylidene fluoride, at least one hexafluoropropylene (HFP)-vinylidene fluoride copolymer, or any combination thereof.

[0083] The electrolyte may be an electrolyte solution, wherein the electrolyte solution may include at least one solvent and at least one electrolyte salt. The at least one solvent in the electrolyte solution may include at least one organic solvent. The at least one organic solvent in the electrolyte may be selected from: propylene carbonate, ethylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), or a mixture thereof.

[0084] The electrolyte may include at least one additive, wherein the at least one additive may be configured to release at least one gas selected from the group consisting of CO2, H2, CO, CH4, or any combination thereof during battery operation. The at least one additive may be selected from the group consisting of vinylene carbonate (VC), vinyl sulfite (ES), and fluoroethylene carbonate (FEC).

[0085] The electrolyte may release at least one gas during use of the battery. The at least one gas may be a decomposition product of the electrolyte.

[0086] The electrolyte may be impregnated within at least one separator.

[0087] The housing wall of the battery housing may include an aperture and the ventilation element according to the second aspect mounted in the aperture.

[0088] It will be appreciated that the features of the battery housing in the first aspect are features of the battery housing of the battery in the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings.

[0090] Figure 1 : A cross-sectional side view of a portion of a battery housing according to one embodiment;

[0091] Figure 2 : A cross-sectional side view of a portion of a battery housing according to one embodiment;

[0092] Figure 3: Test setup for measuring CO2 permeability / transmission rate;

[0093] Figure 4 : Test setup for measuring water permeability / transmission rate;

[0094] Figure 5 : SEM image of an exemplary pore with a maximum width of 5.3 μm in an aluminum substrate;

[0095] Figure 6 : SEM image of exemplary pores with a maximum width of 4.1 μm in a densified expanded polytetrafluoroethylene (ePTFE) substrate;

[0096] Figure 7 : a cross-sectional side view of a ventilation element according to one embodiment; and

[0097] Figure 8 : Cross-sectional side view of a battery housing including a ventilation element according to one embodiment. DETAILED DESCRIPTION

[0098] Although the following detailed description of the manufacture and use of various embodiments of the present invention, it should be understood that the present invention provides many applicable inventive concepts that can be embodied in a variety of specific situations. The specific embodiments discussed herein are merely illustrative of specific ways to manufacture and use the present invention and do not limit the scope of the present invention.

[0099] To facilitate understanding of the present invention, certain terms are defined below. The terms defined herein have the meanings commonly understood by persons of ordinary skill in the art to which the present invention relates. The terms "a," "an," and "the" do not refer to single entities, but rather encompass general categories that may be illustrated using specific examples. The terms herein are used to describe specific embodiments of the present invention, but their use does not limit the present invention, except as described in the claims.

[0100] Test Method

[0101] CO 2 Transmittance

[0102] The CO2 transmission rate through the substrate was determined according to ASTM D1434-82 (Standard Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting). A differential pressure test method was used. The test setup was as follows: Figure 3as shown.

[0103] For samples with a relatively low CO2 permeability of less than 3,000,000 cm 3 / (m 2 ·day·bar), the gas permeability of the substrate was measured using a gas permeability tester (model VAC-V2). The sample substrate was placed on an aluminum mask holder (Mocon part #052-612) with a 5 cm 2 opening at the center. Subsequently, the mask was fixed inside the device test cell and sealed in the chamber. A vacuum was applied for 25 minutes to remove the air in the test chamber. Subsequently, dry CO2 gas was introduced into the chamber and introduced onto the first side of the substrate. For testing, the pressure difference across the entire substrate was adjusted to 1 bar. The CO2 passing through the sample substrate and entering the second side of the substrate was detected to provide the permeability of the substrate. The test temperature was set at 37.8 °C. The proportional parameter was set at 10%. The CO2 permeability was reported by the instrument in units of cm 3 / (m 2 ·day·bar), and converted to a volume value at standard temperature and pressure (temperature 0 °C, pressure 1 bar).

[0104] For samples with a relatively high CO2 permeability, greater than 3,000,000 cm 3 / (m 2 ·day·bar), the gas permeability of the substrate was measured using a gas permeability analyzer GTR series (model #GTR-30XAGR) from GTR Tec Co., Ltd. (Japan) (using Shimadzu GC-2014 gas chromatography). The sample substrate was placed on an aluminum mask holder (Mocon part #052-612) with a 5 cm 2 opening at the center. The mask was cut to approximately 6 x 6 cm. Subsequently, it was fixed inside the instrument measurement cell and sealed in the chamber. A vacuum was applied for 10 minutes to remove the air in the test chamber. Subsequently, dry CO2 gas was introduced into the chamber and introduced onto the first side of the substrate. For testing, the pressure difference across the entire substrate was adjusted to 1 bar. The CO2 passing through the sample substrate and entering the second side of the substrate was detected to provide the permeability of the substrate. The test temperature was set at 37.8 °C. The analyte collection time was set at 5 to 10 seconds, and the GC analysis time was set at 3 minutes. The CO2 permeability was reported by the instrument in units of cm 3 [[ID=2৬]] / (m 2 ·day·atm). It was converted to units of cm 3 / (m 2 ·day·bar) where the volume value is at standard temperature and pressure as defined above.

[0105] Moisture permeability

[0106] The water vapor permeability through the substrate was determined according to ASTM F1249-20 (Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor). The isobaric test method was used. The test setup was as follows: Figure 4 Specifically, the instrument used to test the water vapor transmission rate of the material is an AMETEK / Mocon water vapor permeation analyzer (model Permatran-W 3 / 34). The sample substrate is placed on an aluminum mask holder (Mocon part #052-612) with a 5 cm center. 2 Opening. Subsequently, the mask is fixed to the device test cell and sealed in the chamber. A sample substrate is provided, and the sample chamber is divided into a first part (high humidity chamber) and a second part (low humidity chamber). The first part retains water, thereby producing a high humidity side of the sample substrate. Dry nitrogen is passed through the second side to provide a low humidity side of the sample substrate. Both the first and second parts in the chamber are maintained at ambient pressure. The test is performed on the high humidity side at 100% relative humidity and at 37.8°C. Water vapor passing through the sample substrate is detected at the "dry gas" outlet, from the first side of the substrate on the high humidity side into the second side of the substrate on the low humidity side, thereby measuring the water vapor passing through the sample substrate. The water vapor transmission rate is reported by the instrument in g / (m 2 ·day).

[0107] Water vapor transmission rate converted to unit cm 3 / (m 2 · day·bar), using the ideal gas law and dividing by the water vapor partial pressure difference (0.066 bar), where the volume is converted to volume at standard temperature and pressure as described above. Both carbon dioxide (CO2) transmission rate and water vapor (moisture) transmission rate (in cm 3 / (m 2 Both the Japanese and the British pound (Brazil) are used to calculate the ratio of the carbon dioxide (CO2) transmission rate to the water vapor (moisture) transmission rate by dividing the CO2 transmission rate by the water vapor transmission rate, where the volume is converted to volume at standard temperature and pressure as described above. The ratio of the CO2 transmission rate to the water vapor transmission rate is unitless (i.e., dimensionless).

[0108] Physical parameters

[0109] The surface area of the pores was calculated from the SEM images using image analysis. The effective diameter of the pores was calculated from the measured pore area on the laser exit side. The maximum width of the pores was estimated from the SEM images using image analysis.

[0110] The thickness of the polymer film substrate was measured using a Mitutoyo Litematic VL50S thickness gauge. The thickness of the aluminum foil substrate was measured using a Mitutoyo 547-400S Digimatic thickness gauge.

[0111] refer to Figure 1 The battery housing 1 comprises a housing wall 2, three holes 4 formed in the housing wall 2, a first protective layer 6 (serving as at least one protective element), and a second protective layer 8 (serving as additional at least one protective element).

[0112] The housing wall 2 comprises an aluminum (Al) foil having a thickness of 29.3 μm and three apertures 4 extending through the housing wall 2 from a first side 10 to a second side 12. The three apertures 4 have a generally circular cross-section with a diameter (corresponding to a maximum width) of 4 μm. A first protective layer 6 and a second protective layer 8 comprise expanded polytetrafluoroethylene (ePTFE). The first protective layer 6 is disposed on the first side 10, and the second protective layer 8 is disposed on the second side 12. The first protective layer 6 and the second protective layer 8 cover the three apertures 4 to prevent particulate matter from entering or clogging one or more of the three apertures 4, thereby ensuring that the three apertures 4 can vent any gas that may be generated within the battery housing 1.

[0113] refer to Figure 2 The battery pouch 20 (serving as the battery housing) includes a pouch wall 22 (serving as the housing wall) and a hole 24 formed in the pouch wall 22. The pouch wall 22 has a thickness of 100 μm and includes an aluminum foil 26, a polyethylene terephthalate (PET) layer 28 facing the outside of the battery pouch, and a polypropylene layer 30 facing the inside of the battery pouch. The aluminum foil 26 is disposed between the polyethylene terephthalate layer 28 and the polypropylene layer 30. The hole 24 has a generally elliptical cross-section with a maximum width of 12 μm.

[0114] exist Figure 2 In an alternative embodiment shown in , a first protective layer and a second protective layer are provided over the holes 24 to prevent the holes 24 from being blocked by, for example, particulate matter. The first and second protective layers comprise expanded ultra-high molecular weight polyethylene.

[0115] refer to Figure 7Ventilation element 100 includes a densified ePTFE substrate 102 (serving as an impermeable substrate), a first ePTFE membrane 104 (serving as a first protective element), and a second ePTFE membrane 106 (serving as a second protective element). A single 5 μm hole 108 is drilled through substrate 102. Substrate 102 is 25 μm thick. First ePTFE membrane 104 and second ePTFE membrane 106 block hole 108 on first side 110 and second side 112 of substrate 102, respectively.

[0116] refer to Figure 8 , the ventilation element 100 is mounted over the aperture 114 in the battery housing 116 .

[0117] Example

[0118] Specific exemplary embodiments are provided in Table 1 and the measured properties of those examples are provided in Table 2.

[0119] Hereinafter, the PTFE substrate materials used in Examples 1 and 2 were prepared using the following method.

[0120] PTFE resin was mixed with a lubricant (Isopar K, Exxon, Houston, TX) at a concentration of 0.167 g / g, followed by stirring, compression into cylindrical pellets, and heat conditioning at 70°C for 24 hours. The cylindrical pellets were then extruded through a rectangular die at a compression ratio of 88 into a tape having a thickness of 0.711 mm. The resulting tape was then dried to remove the lubricant.

[0121] The dried PTFE tape was then expanded between heated drums in the y-direction at a linear rate of about 46% / sec, a drum temperature of 315°C, and a stretch equal to 1,032%. The tape was then expanded in the x-direction at a linear rate of about 56% / sec, a temperature of about 300°C, and a stretch equal to 2,863%. The resulting product had a density of about 0.20 g / cm 3 Unsintered expanded PTFE membrane.

[0122] Based on the disclosures of U.S. Pat. Nos. 5,374,473 and 7,521,010 B2, the resulting unsintered expanded PTFE membrane was compressed and densified at a temperature of 370° C. and a pressure of 1724 kPa (250 psi). The resulting article was a sintered and densified ePTFE membrane having a thickness of approximately 24 μm.

[0123] Table 1: Exemplary substrates according to specific embodiments

[0124]

[0125]

[0126] In Examples 2, 4, 6, 7-14, 16, and 17 above, the holes were formed by laser drilling, and the effective hole size referred to in Table 1 above refers to the side of the substrate opposite to the side to which the laser was applied to form the holes (i.e., the side from which the laser "exits" the substrate). In Example 15, the holes were formed by mechanical drilling using a 50 μm drill bit.

[0127] 50 μm thick PCTFE membrane was obtained from Honeywell (Hydroblock P2000TR1). 500 μm polypropylene film was obtained from McMaster-Carr (part #5895N112). 25 μm and 50 μm thick aluminum foils were obtained from Grainger (part #4UGH8 and #4UGJ1). 100 μm aluminum foil was obtained from McMaster-Carr (part #9708K54). 400 μm aluminum sheet (6061-T6) was obtained from Xometry Supplies (nominal thickness from the manufacturer).

[0128] The composite film PP-Al-nylon-PET is a standard material for pouch battery casings. It was obtained from Dai Nippon Printing Co., Ltd. (part #D-EL408PH). The total thickness is 153 μm, with aluminum approximately 40 μm thick, polypropylene approximately 80 μm, PET approximately 12 μm, and nylon approximately 15 μm.

[0129] Table 2: Performance of specific examples

[0130]

[0131]

[0132] TR = Transmission Rate, calculated for a volume of gas at standard temperature and pressure, as defined herein.

[0133] As can be seen above, embodiments comprising pores having a maximum width of at least 4 μm provide significantly higher CO2 transmission rates through substrates forming battery housings compared to embodiments without pores, wherein the selectivity of CO2 transmission rates over water vapor transmission rates is significantly increased.

[0134] While intended embodiments of the invention have been described hereinabove, many and various changes and modifications in form, design, structure and arrangement of parts may be made to other embodiments without departing from the invention, and it is understood that all such changes and modifications are considered embodiments as part of the invention as defined in the appended claims.

Claims

1. A battery housing comprising a housing wall comprising an impermeable substrate and at least one hole provided in the impermeable substrate, the hole or each hole extending from a first side of the impermeable substrate to a second side of the impermeable substrate, and the maximum width of the hole or each hole is 0.1 μm to 100 μm, wherein The housing wall has a ratio of carbon dioxide (CO2) transmission rate to water vapor (moisture) transmission rate of at least 2, as measured using the test method described herein.

2. The battery housing of claim 1, wherein the battery housing defines an enclosed space, and the enclosed space retains an electrolyte.

3. A battery housing as claimed in claim 1 or claim 2, wherein the CO2 permeability through the housing wall is at least 25 cm 3 / (day).

4. A battery housing according to any preceding claim, wherein the ratio of the CO2 permeability to the moisture permeability of the housing wall is at least 3.

5. A battery casing according to any preceding claim, wherein the impermeable substrate has a thickness between the first and second sides, and the ratio of the thickness of the impermeable substrate to the cross-sectional area of the or each pore is at least 0.1 / μm.

6. A battery casing as claimed in any preceding claim in which the or each aperture has a maximum width of from 1 to 10 μm.

7. A battery casing as claimed in any preceding claim wherein the or each pore has an effective diameter of from 0.1 μm to 100 μm.

8. A battery casing according to any preceding claim, wherein the battery casing comprises at least one protective element disposed on at least one of the first and second major surfaces of the non-permeable substrate and covering the or each aperture.

9. The battery housing of claim 8, wherein the battery housing comprises two protective elements.

10. A battery housing according to claim 9, wherein the two protective elements comprise a first protective element provided on the first major surface, and a second protective element provided on the second major surface, such that the or each aperture is covered by the first and second protective elements.

11. The battery housing of any one of claims 8 to 10, wherein the at least one protective element comprises a material having a higher CO2 permeability than the housing wall.

12. The battery housing of any one of claims 8 to 11, wherein the at least one protective element comprises an expanded polymer.

13. The battery housing of claim 12, wherein the at least one protective element comprises expanded polytetrafluoroethylene or expanded polyethylene.

14. A ventilation element comprising an impermeable substrate, a first protective element, and a second protective element, wherein the impermeable substrate comprises at least one pore, the pore or each pore extending from a first side of the impermeable substrate to a second side of the impermeable substrate, and wherein the maximum width of the pore or each pore is from 0.1 μm to 100 μm, the first protective element being positioned on the first side of the impermeable substrate to block the pore or each pore, and the second protective element being positioned on the second side of the impermeable substrate to block the pore or each pore.

15. The ventilation element of claim 14, wherein the ventilation element has a ratio of carbon dioxide (CO2) transmission rate to water vapor (moisture) transmission rate of at least 2 using the test method described herein.

16. A ventilation element as claimed in claim 14 or claim 15, wherein the first and second protective elements comprise an expanded polymer selected from expanded polytetrafluoroethylene and expanded polyethylene.

17. A ventilation element as claimed in any one of claims 14 to 16, wherein each of the first and second protective elements has a higher CO2 permeability than the or each aperture.

18. A ventilation element according to any one of claims 14 to 17, wherein the impermeable substrate has a thickness between the first and second sides, and the ratio of the thickness of the impermeable substrate to the cross-sectional area of the or each pore is at least 0.1 / μm.

19. A ventilation element as claimed in any one of claims 14 to 18, wherein the or each aperture has a maximum width of from 1 to 10 μm.

20. A ventilation element as claimed in any one of claims 14 to 16, wherein the or each aperture has an effective diameter of from 0.1 μm to 100 μm.

21. A ventilation element according to any one of claims 14 to 20, wherein the CO2 transmission rate through the ventilation element is at least 25 cm 3 / (day).

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