Improved battery housings including a vent element and methods of preparing a battery including the battery housing

Abstract

A method of preparing a battery, the method comprising the steps providing a battery housing comprising a formation vent; adding an electrolyte to the battery housing to form a battery; retaining the electrolyte within the battery housing for a period; and applying charge across the pair of electrodes to thereby pre-charge the battery; wherein gas generated within the battery housing during the retaining step and pre-charging step is vented out of the battery housing through the at least one hole. Batteries formed by the method and formation vents included in the batteries are also described.

Description

[0001] Improved Battery Housings Including a Vent Element and Methods of Preparing a Battery Including the Battery Housing

[0002] Field

[0003] The present disclosure relates to vent elements, battery housings comprising the vent element and methods of preparing batteries.

[0004] Background

[0005] The provision of improved batteries is increasingly important, especially for mobile electronic devices and for electric vehicles, for example.

[0006] Batteries that have a prismatic can housing or a flexible pouch housing are typically prepared in very specific conditions that ensure that water, either water vapour or liquid water, does not enter the battery housing during the assembly, aging and pre-charging of the battery. Typically, the necessary rigorous conditions involved require the use of a dry room that is expensive to operate.

[0007] Typically, during the preparation process gas is generated within the battery housing during the pre-charge step. The battery housing needs to be sealed during the pre-charge step and therefore the gas generated aggregates within the battery housing increasing the pressure within the battery housing. Before the battery is shipped it is necessary to vent the gas from within the battery housing. Accordingly, the seal for the battery housing is broken to allow the gas to be released under vacuum, typically, and then re-sealed.

[0008] Accordingly, there are a number of steps that need to be followed and that need to be carried out under rigorous conditions, resulting into high operating costs.

[0009] For larger capacity battery cells (greater than 100 Ah battery cells, for example) a single aperture in the battery housing is used to both inject electrolyte into the battery housing and to vent gas, and the single aperture is typically plugged during the pre-charging process. The plug is then removed to allow venting of the battery housing, which often results in electrolyte leakage. Once venting under vacuum has been completed, any leaked electrolyte is cleaned from the battery housing and additional electrolyte is added to the battery housing to make up for the leaked electrolyte before the aperture is sealed. The entirety of this process must be carried out under strict dry conditions. Alternatively, battery pouch cells that comprise a flexible battery housing often comprise an additional portion that is specifically provided to be breached or pierced after the pre-charge step to allow gas that has built up within the battery housing to be vented. Once the battery housing has been vented the breached or pierced portion is sealed from the remaining portion of the battery housing and the removed. Accordingly, a flexible battery housing has to be larger than required for the final battery pouch cell to be produced incurring additional material cost.

[0010] It is desirable to provide improved methods of forming batteries that reduce the operational costs of the battery forming process.

[0011] Accordingly, at least one aspect of the present disclosure is directed to providing improved methods of forming batteries, or improved battery housings.

[0012] Summary

[0013] According to a first aspect there is provided a venting element comprising a non-permeable substrate, and a first protective element , the non-permeable substrate comprising at least one hole, the or each hole extending from a first side of the non-permeable substrate to a second side of the non-permeable substrate and the or each hole has a maximum width of from 1 pm to 50 pm, the first protective element being positioned on the first side of the non-permeable substrate occluding the or each holes.

[0014] As used herein, the term "maximum width” refers to the major cross-sectional dimension of the or each hole. For example, for a hole that has a circular cross-section the maximum width refers to the diameter of the circular cross-section.

[0015] The or each hole may have a maximum width of from 1 pm to 40 pm. The or each hole may have a maximum width of from 1 pm to 30 pm. The or each hole may have a maximum width of from 1 pm to 20 pm. The or each hole may have a maximum width of from 1 pm to 15 pm. The or each hole may have a maximum width of from 1 pm to 10 pm. The or each hole may have a maximum width of from 1 pm to 9 pm. The or each hole may have a maximum width of from 1 pm to 8 pm. The or each hole may have a maximum width of from 1 pm to 7 pm. The or each hole may have a maximum width of from 1 pm to 6 pm. The or each hole may have a maximum width of from 1 pm to 5 pm. The or each hole may have a maximum width of from 5 pm to 50 pm. The or each hole may have a maximum width of from 10 pm to 50 pm. The or each hole may have a maximum width of from 15 pm to 50 pm. The or each hole may have a maximum width of from 10 pm to 30 pm. The or each hole may have an effective diameter of less than 50 pm. The or each hole may have an effective diameter of less than 40 pm. The or each hole may have an effective diameter of less than 20 pm.

[0016] The or each hole may have an effective diameter of from 1 pm to 50 pm. The or each hole may have an effective diameter of from 1 pm to 40 pm. The or each hole may have an effective diameter of from 1 pm to 30 pm. The or each hole may have an effective diameter of from 1 pm to 20 pm. The or each hole may have an effective diameter of from 1 pm to 15 pm. The or each hole may have an effective diameter of from 5 pm to 50 pm. The or each hole may have an effective diameter of from 10 pm to 50 pm. The or each hole may have an effective diameter of from 10 pm to 30 pm.

[0017] As used herein, the term “effective diameter” refers to the diameter of the or each hole if it is approximated to be circular from a measured cross-sectional area.

[0018] As used herein, the term “hole” refers to a pathway or channel that allows passage of fluid from a first side of a substrate to a second side of that substrate. The pathway may be linear such that fluid may pass in a substantially straight line through the substrate. The term “hole” as used herein does not include pores that provide a tortuous pathway through a porous substrate, but rather are more direct.

[0019] The or each hole may form a direct pathway through the non-permeable substrate. The or each hole may be formed in or through the non-permeable substrate after the non-permeable substrate has been formed. Accordingly, the or each hole is not a pore of a porous material, for example.

[0020] 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 having any number of sides such as a triangular, rectangular (square or oblong), pentagonal, hexagonal or octagonal. The or each hole may have an irregular cross- sectional shape.

[0021] The or each hole may comprise an approximately cylindrical portion. The or each hole may be approximately cylindrical. Accordingly, 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 to the second side of the non-permeable substrate.

[0022] The or each hole may comprise an approximately conical portion. The or each hole may be approximately conical. Accordingly, the maximum width of the or each hole may increase or reduce as the or each hole extends from the first side to the second side.

[0023] The maximum width of the at least one hole on the first side of the non-permeable substrate may be different to the maximum width on the second side of the non-permeable substrate.

[0024] The maximum width of the at least one hole on the first side of the non-permeable substrate may be at least 30% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be at least 40% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be at least 50% larger than the maximum width of the at least one hole on the second side of the non- permeable substrate.

[0025] The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 75% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 50% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 40% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 35% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 20% to 75% larger than the maximum width of the at least one hole on the second side of the non- permeable substrate. The maximum width of the at least one hole on the first side of the non- permeable substrate may be from 25% to 75% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 30% to 75% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be at least 30% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be at least 40% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be at least 50% smaller than the maximum width of the at least one hole on the second side of the non- permeable substrate.

[0026] The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 75% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 50% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 40% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 10% to 35% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 20% to 75% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 25% to 75% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate. The maximum width of the at least one hole on the first side of the non-permeable substrate may be from 30% to 75% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate.

[0027] The CO2 transmission rate through the venting element may be at least 10 ml / hour. The CO2 transmission rate through the venting element may be at least 20 ml / hour. The CO2transmission rate through the venting element may be at least 30 ml / hour. The CO2transmission rate through the venting element may be at least 40 ml / hour. The CO2 transmission rate through the venting element may be at least 50 ml / hour. The CO2 transmission rate through the venting element may be at least 75 ml / hour. The CO2 transmission rate through the venting element may be at least 100 ml / hour. The CO2transmission rate through the venting element may be at least 150 ml / hour. The CO2 transmission rate through the venting element may be from 10 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 20 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 30 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 40 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 50 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 75 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 100 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 200 ml / hour to 2000 ml / hour. The CO2 transmission rate through the venting element may be from 10 ml / hour to 1500 ml / hour. The CO2 transmission rate through the venting element may be from 10 ml / hour to 1000 ml / hour. The CO2 transmission rate through the venting element may be from 10 ml / hour to 750 ml / hour. The CO2 transmission rate through the venting element may be from 10 ml / hour to 500 ml / hour.

[0028] The CO2 transmission rate may be indicative of the transmission rate of other gases having a similar molecular weight to CO2. Other example gases that may be relevant to the venting element during use may include hydrogen gas (H2), methane (CH4), ethane (C2H6), ethylene (C2H4), propane (CsHs), propylene (CsHe), or carbon monoxide (CO).

[0029] The water vapor transmission rate through the venting element may be less than 2.0 mg / hour. The water vapor transmission rate through the venting element may be less than 1.0 mg / hour. The water vapor transmission rate through the venting element may be less than 0.5 mg / hour. The water vapor transmission rate through the venting element may be less than 0.1 mg / hour.

[0030] The water vapor transmission rate through the venting element may be from 3.0 mg / hour to 0.0001 mg / hour. The water vapor transmission rate through the venting element may be from 2.5 mg / hour to 0.0001 mg / hour. The water vapor transmission rate through the venting element may be from 2.0 mg / hour to 0.0001 mg / hour. The water vapor transmission rate through the venting element may be from 1.0 mg / hour to 0.0001 mg / hour. The water vapor transmission rate through the venting element may be from 0.75 mg / hour to 0.0001 mg / hour. The water vapor transmission rate through the venting element may be from 0.5 mg / hour to 0.0001 mg / hour. The water vapor transmission rate through the venting element may be from 0.01 mg / hour to 0.0001 mg / hour. It will be appreciated that for the current disclosure it is desirable that the water vapor transmission rate is as low as possible, to minimise or effectively prevent transmission of water vapor across the venting element.

[0031] The water vapor transmission rate through the venting element may be dependent on the direction through the venting element. In embodiments where the maximum width of the at least one hole on the first side of the non-permeable substrate is different to the maximum width of the at least one hole on the second side of the non-permeable substrate, the water vapor transmission rate through the venting element from the first side of the non-permeable substrate to the second side of the non-permeable substrate may be different to the water vapor transmission rate through the venting element from the second side of the non- permeable substrate to the first side of the non-permeable substrate. The water vapor transmission rate may be greater from the side of the non-permeable substrate where the at least one hole has the largest maximum width to the side of the non-permeable substrate where the at least one hole has the smallest maximum width.

[0032] The at least one hole may have a first end adjacent to the first side of the non-permeable substrate and a second end adjacent to the second side of the non-permeable substrate, the first end having a first maximum width and the second end having a second maximum width, wherein the first maximum width may be larger than the second maximum width.

[0033] In embodiments where the at least one hole has a first end and a second end having a maximum width different to the first end the CO2 transmission rate to water vapour transmission rate ratio from first end to the second end of at least 3. In embodiments where the first end has a maximum width that is smaller than the second end, the CO2 transmission rate to water vapour transmission rate ratio from first end to the second end of at least 3.

[0034] The CO2 transmission rate to water vapour transmission rate ratio from the first side of the non-permeable substrate to the second side of the non-permeable substrate is at least 3.

[0035] The CO2 transmission rate to water vapour transmission rate ratio from the second side of the non-permeable substrate to the first side of the non-permeable substrate is at least 3.

[0036] As used herein, the “CO2 transmission rate to water vapor transmission rate ratio” is calculated by dividing CO2 transmission rate by water vapor transmission rate for a substrate. CO2 transmission to water vapor transmission ratio has no units (i.e., is dimensionless). Accordingly, a ratio of at least 2 means that at least twice the volume of CO2 is transmitted through the housing wall to that of water vapor at a given pressure.

[0037] The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be at least 5. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be at least 10. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be at least 15. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be at least 20. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be at least 30. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be at least 40. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be at least 50.

[0038] The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 5 to 2000. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 10 to 2000. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 15 to 2000. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 20 to 2000. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 30 to 2000. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 40 to 2000. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 50 to 2000. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 5 to 1500. The CO2 transmission rate to water vapour transmission rate ratio through the venting element may be from 5 to 1000.

[0039] The or each hole may be formed within the non-permeable substrate by any suitable method. The or each hole may be formed by mechanical drilling. The or each hole may be formed by laser drilling. In embodiments where the or each hole are formed by laser drilling the maximum width of the or each hole may slightly reduce from a first side that the laser is incident to a second side as the laser is attenuated through the non-permeable substrate. Accordingly, the or each hole may have a first maximum width or effective diameter on the first side of the non- permeable substrate and the or each hole may have a second maximum width or effective diameter on the second side of the non-permeable substrate. The first maximum width or effective diameter may be larger than the second maximum width or effective diameter. The first maximum width or effective diameter may be smaller than the second maximum width or effective diameter. The or each hole may be formed by puncturing the non-permeable substrate. The or each hole may be formed by puncturing the non-permeable substrate by pushing or urging a puncturing element through the non-permeable substrate. The puncturing element may be a needle, capillary tube or similar.

[0040] In embodiments where more than one hole are provided in the non-permeable substrate, the more than one hole may be formed by an array of puncturing elements. The puncturing elements may be arranged in a regular pattern such that the more than one hole thereby provided in the non-permeable substrate are arranged in a regular pattern.

[0041] The first protective element may comprise an expanded polymer selected from expanded polytetrafluoroethylene and expanded polyethylene.

[0042] The venting element may comprise a second protective element being positioned on the second side of the non-permeable substrate occluding the or each hole.

[0043] Each of the first protective element and the second protective element where present may have a higher CO2 transmission rate than the or each hole.

[0044] Each of the first protective element, and the second protective element where present, may have an airflow of at least 20 ml / h. Each of the first protective element, and the second protective element where present, may have an airflow of at least 40 ml / h. Each of the first protective element, and the second protective element where present, may have an airflow of at least 60 ml / h. Each of the first protective element, and the second protective element where present, may have an airflow of at least 80 ml / h. Each of the first protective element, and the second protective element where present, may have an airflow of at least 100 ml / h. Each of the first protective element, and the second protective element where present, may have an airflow of at least 150 ml / h. Each of the first protective element, and the second protective element where present, may have an airflow of at least 200 ml / h.

[0045] Each of the first protective element, and the second protective element where present, may have an airflow of from 10 ml / hour to 1000 ml / hour. Each of the first protective element, and the second protective element where present, may have an airflow of from 20 ml / hour to 1000 ml / hour. Each of the first protective element, and the second protective element where present, may have an airflow of from 30 ml / hour to 1000 ml / hour. Each of the first protective element, and the second protective element where present, may have an airflow of from 40 ml / hour to 1000 ml / hour. Each of the first protective element, and the second protective element where present, may have an airflow of from 50 ml / hour to 1000 ml / hour. Each of the first protective element, and the second protective element where present, may have an airflow of from 100 ml / hour to 1000 ml / hour. Each of the first protective element, and the second protective element where present, may have an airflow of from 200 ml / hour to 1000 ml / hour.

[0046] As used herein, the term “non-permeable substrate” refers to a substrate that has a low water vapor transmission rate. As used herein, a low water (moisture) vapor transmission rate is understood to be a moisture vapor transmission rate of less than 5 g / (m2day) at 100% relative humidity at 40°C or 100,000 cm3 / (m2day bar).

[0047] The non-permeable substrate may comprise a polymer. The polymer may be a fluoropolymer. The polymer may be a non-fluoropolymer. The polymer may be an expanded polymer. The polymer may be a densified expanded polymer.

[0048] For the avoidance of doubt, the term “densified expanded polymer membrane” refers to a polymer membrane that has been expanded below its melting temperature and then after expansion has been densified. Accordingly, it will be understood that the density of the at least one densified expanded polymer membrane is greater than the density of a corresponding expanded polymer membrane that has not been densified. It will be understood to the person skilled in the art that a polymer membrane that has been expanded below its melting temperature and then densified may have a lower porosity than a corresponding polymer membrane of the same material that has been expanded but has not been densified. The step of densification may close a proportion of the pores in the expanded polymer membrane. Therefore, the degree to which an expanded polymer membrane has been densified may allow the permeation of gases across that membrane to be controlled and tailored to the required use.

[0049] The polymer may be selected from polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), perfluoro(alkylvinyl ether) (“PAVE”, including perfluoro(methylvinyl ether), perfluoro(ethylvinyl ether), perfluoro(propylvinyl ether) etc), vinylidene fluoride (VDF), fluorinated ethylene propylene (FEP), chlorotrifluoroethylene (CTFE) or co-polymers or combinations thereof. The polymer may be selected from polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyamide, or copolymers of the same.

[0050] The non-permeable substrate may comprise a metal. For example, the non-permeable substrate may comprise aluminium, iron, copper, tin, or alloys or combinations thereof.

[0051] The non-permeable substrate may have a thickness between the first side and the second side. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 2. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 3. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 5. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 7. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 10. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 15. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 20. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 25. Accordingly, the ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 3, 5, 7, 10, 15, 20, 25 or values in between.

[0052] The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 2 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 3 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 5 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 7 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 10 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 15 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 20 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 25 to 100. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 2 to 90. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 2 to 80. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 2 to 70. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be from 2 to 60. In embodiments where the at least one hole is straight (the maximum width of the at least one hole on the first side of the non-permeable substrate is approximately the same as the maximum width of the at least one hole on the second side of the non-permeable substrate) the ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 10. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 15. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 20.

[0053] In embodiments where the at least one hole is tapered (the maximum width of the at least one hole on the first side of the non-permeable substrate is different to the maximum width of the at least one hole on the second side of the non-permeable substrate) the ratio of the non- permeable substrate thickness to the average maximum width of the or each hole may be at least 2. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 5. The ratio of the non-permeable substrate thickness to the maximum width of the or each hole may be at least 10.

[0054] The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be at least 0.1 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be at least 0.5 per pm. The ratio of the non- permeable substrate thickness to the cross-sectional area of the or each hole may be at least 0.6 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be at least 0.7 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be at least 0.8 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be at least 0.9 per pm. The ratio of the non-permeable substrate thickness to the cross- sectional area of the or each hole may be at least 1 per pm.

[0055] The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be from 0.1 to 1000 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be from 0.1 to 750 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be from 0.1 to 500 per pm. The ratio of the non-permeable substrate thickness to the cross- sectional area of the or each hole may be from 0.1 to 250 per pm. The ratio of the non- permeable substrate thickness to the cross-sectional area of the or each hole may be from 0.1 to 100 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be from 0.5 to 1000 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be from 1 to 1000 per pm. The ratio of the non-permeable substrate thickness to the cross-sectional area of the or each hole may be from 2 to 1000 per pm.

[0056] In a second aspect there is provided a battery comprising a housing wall, the housing wall comprising a non-permeable substrate and at least one hole provided in the non-permeable substrate, the or each hole extends from a first side of the non-permeable substrate to a second side of the non-permeable substrate and the or each hole has a maximum width of from 1 pm to 50 pm.

[0057] The battery may be a battery pouch cell or a battery prismatic cell.

[0058] The housing wall may comprise at least one of: a metal, a metal alloy, at least one polymer, or a combination thereof.

[0059] The at least one polymer may comprise a fluoropolymer such as PTFE, PFA, FEP or a non- fluoropolymer such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) or copolymers thereof.

[0060] The housing wall may comprise at least one metallic layer and at least one polymer layer.

[0061] The housing wall may comprise a vent aperture and the non-permeable substrate may occlude the vent aperture. A venting element according to the first aspect may occlude the vent aperture and the at least one hole of the venting element may correspond to the at least one hole of the non-permeable substrate of the present aspect. The venting element may form a plug that is configured to removably occlude or plug the vent aperture. The venting element may comprise a sealing element around the periphery of the venting element and the sealing element may be configured to form a seal between the venting element and the housing wall around the periphery of the vent aperture. Accordingly, the at least one hole of the venting element is the sole pathway for gas to pass from the interior of the battery housing to the exterior of the battery housing. The venting element may comprise a handle element that is configured to allow the venting element to be readily gripped and removed form the vent aperture.

[0062] The housing wall may comprise at least two holes provided in the non-permeable substrate. The housing wall may comprise at least three holes provided in the non-permeable substrate. The housing wall may comprise at least four holes provided in the non-permeable substrate. The housing wall may comprise at least five holes provided in the non-permeable substrate. The housing wall may comprise at least six holes provided in the non-permeable substrate. The housing wall may comprise at least seven holes provided in the non-permeable substrate. The housing wall may comprise at least eight holes provided in the non-permeable substrate. The housing wall may comprise at least nine holes provided in the non-permeable substrate. The housing wall may comprise at least ten holes provided in the non-permeable substrate.

[0063] The housing wall may comprise from 1 to 100 holes provided in the non-permeable substrate.

[0064] The housing wall may comprise from 1 to 75 holes provided in the non-permeable substrate, The housing wall may comprise from 1 to 50 holes provided in the non-permeable substrate, The housing wall may comprise from 1 to 40 holes provided in the non-permeable substrate, The housing wall may comprise from 1 to 30 holes provided in the non-permeable substrate,

[0065] The housing wall may comprise from 1 to 20 holes provided in the non-permeable substrate, The housing wall may comprise from 1 to 15 holes provided in the non-permeable substrate.

[0066] The housing wall may comprise from 1 to 10 holes provided in the non-permeable substrate.

[0067] In some embodiments the housing wall may have one hole provided in the non-permeable substrate. In some embodiments the housing wall may have two holes provided in the non- permeable substrate. In some embodiments the housing wall may have three holes provided in the non-permeable substrate. In some embodiments the housing wall may have four holes provided in the non-permeable substrate. In some embodiments the housing wall may have five holes provided in the non-permeable substrate.

[0068] The battery may be a secondary battery. The secondary battery may be a lithium-ion battery.

[0069] As used herein, the term “lithium-ion battery” is any battery where lithium-ions are configured to move between a negative electrode and a positive electrode during operation of the battery. 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.

[0070] The positive electrode may be chosen from: Lithium Nickel Manganese Cobalt Oxide (“NMC”), Lithium Nickel Cobalt Aluminum Oxide (“NCA”), Lithium Manganese Oxide (“LMO”), Lithium Iron Phosphate (“LFP”), Lithium Cobalt Oxide (“LCO”), or any combination thereof.

[0071] The negative electrode may be chosen from: Lithium, Graphite, Lithium Titanate (“LTO”), a Tin-Cobalt alloy, or any combination thereof. In some embodiments, the battery may comprise at least one separator. The at least one separator may comprise at least one material chosen from 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.

[0072] The electrolyte may be an electrolytic solution, wherein the electrolytic solution may comprise at least one solvent and at least one electrolytic salt. The at least one solvent of the electrolytic solution may comprise at least one organic solvent. The at least one organic solvent of the electrolyte may be chosen from propylene carbonate, ethylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), or mixtures thereof.

[0073] Whilst it is desirable for the electrolyte to solely act as an electrolyte within the battery housing and facilitate the transport of ions between the electrodes, the electrolyte may degenerate during use of the battery. The electrolyte may be involved in side chemical reactions to generate side products. The side products may include gases such as CO2, H2, CO, CH4, C2H6, C2H4, C3H6, or CsHs.

[0074] The electrolyte may comprise at least one additive, wherein the at least one additive may be configured to release the at least one gas chosen from CO2, H2, CO, CH4 or any combination thereof during operation of the battery. The at least one additive may be selected from the group comprising vinylene carbonate (VC), ethylene sulfite (ES), and fluoroethylene carbonate (FEC).

[0075] The electrolyte may be impregnated within the at least one separator.

[0076] In some embodiments the housing wall may be rigid. Accordingly, the housing wall may be configured to resist deformation to thereby change the shape of the housing wall. Alternatively, the housing wall may be flexible. Accordingly, the housing wall may be configured to at least partially deform to thereby change the shape of the housing wall. For example, the housing wall may be a pouch-type housing wall and the battery housing may be a battery pouch.

[0077] In some embodiments, the housing wall may comprise at least one of: a metal, a metal alloy, or a combination thereof. In some embodiments, the housing wall may comprise at least one of: Iron (Fe), Aluminum (Al), or alloys thereof. In some embodiments, the housing wall may comprise at least one polymer. The at least one polymer may comprise a fluoropolymer such as PTFE, PFA, FEP or copolymers thereof. The at least one polymer may comprise a non- fluoropolymer such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) or copolymers thereof. The housing wall may comprise a combination of at least one metal layer and at least one polymer layer. The housing wall may comprise at least one metal layer provided in between at least two polymer layers. Accordingly, the housing wall may comprise at least one metal layer with at least one polymer layer provided on a first side of the at least one metal layer and at least one polymer layer provided on a second side of the at least one metal layer. The at least one metal layer may thereby be protected by the at least one polymer layer on the first side and 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 comprise 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 to 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 to the at least one polymer layer on the second side.

[0078] In embodiments where the housing wall comprises multiple layers, it is to be understood that the or each holes may extend through each of the multiple layers to form through holes through the housing wall. Accordingly, in embodiments where the at least one hole extends through the housing wall or through a venting element provided across an aperture in the housing wall, the at least one hole extends though the full thickness of the housing wall or the venting element such that gas may be transmitted from the interior of the housing wall to the exterior of the housing wall.

[0079] The at least one hole may be approximately conical and the maximum width on the first side of the non-permeable substrate may be different to the maximum width on the second side of the non-permeable substrate.

[0080] The maximum width of the at least one hole on the first side of the non-permeable substrate may be larger than the maximum width of the at least one hole on the second side of the non- permeable substrate.

[0081] The maximum width on the first side of the non-permeable substrate may be at least 30% larger than the maximum width on the second side of the non-permeable substrate. The first side of the non-permeable substrate may face away from the battery housing, or the first side of the non-permeable substrate may face into the battery housing.

[0082] The battery housing may comprise at least one protective element provided on at least one of a first major surface and a second major surface of the non-permeable substrate and covers the or each hole.

[0083] The battery housing may comprise two protective elements.

[0084] The two protective elements may 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 hole is covered by the first protective element and the second protective element.

[0085] The at least one protective element may comprise an expanded polymer.

[0086] The at least one protective element may comprise expanded polytetrafluoroethylene (ePTFE) or expanded polyethylene (ePE).

[0087] The battery housing may comprise at least one protective element provided on at least one of the first side and the second side of the non-permeable substrate and may cover the or each hole. The at least one protective element may prevent the ingress of particulates into the or each hole. The at least one protective element may prevent the ingress of liquids into the or each hole. The battery housing may comprise two protective elements. The two protective elements may comprise a first protective element provided on the first side and a second protective element provided on the second side such that the or each hole is covered by both the first protective element and the second protective element. Accordingly, the a first end of the or each hole may be covered by the first protective element and a second end of the or each hole may be covered by the second protective element.

[0088] The at least one protective element may comprise an open material.

[0089] As used herein, the term “open material” refers to a material that has high porosity and a low resistance to gas flow through it. In the context of the present aspect, an open material has a higher CO2 transmission rate through it than the housing wall so as not to limit the CO2 transmission rate through the or each hole within the non-permeable substrate of the housing wall. The at least one protective element may comprise a highly porous material. The at least one protective element may comprise a material that has a higher CO2 transmission rate than the housing wall. Accordingly, the CO2 transmission rate across the battery housing is not limited by the at least one protective element and is rather limited by the CO2 transmission rate of the housing wall. The at least one protective element may have a CO2 transmission rate of at least 200,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of at least 300,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of at least 400,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of at least 500,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of at least 600,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of at least 700,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of at least 800,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of at least 1 ,000,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of from about 200,000,000 cm3 / (m2day bar) to about 50,000,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of from about 300,000,000 cm3 / (m2day bar) to about 50,000,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of from about 400,000,000 cm3 / (m2day bar) to about 50,000,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of from about 500,000,000 cm3 / (m2day bar) to about 50,000,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of from about 600,000,000 cm3 / (m2day bar) to about 50,000,000,000 cm3 / (m2day bar).

[0090] The at least one protective element may have a CO2 transmission rate of from about 700,000,000 cm3 / (m2day bar) to about 50,000,000,000 cm3 / (m2day bar). The at least one protective element may have a CO2 transmission rate of from about 800,000,000 cm3 / (m2day bar) to about 50,000,000,000 cm3 / (m2day bar).

[0091] According to a third aspect there is provided a method of preparing a battery, the method comprising the steps: providing a battery housing comprising a formation vent within a housing wall, and a pair of electrodes, the formation vent comprising a non-permeable substrate and at least one hole provided in the non-permeable substrate, the at least one hole having a maximum width of from 1 pm to 50 pm; adding an electrolyte to the battery housing to form a battery; and applying charge across the pair of electrodes to thereby pre-charge the battery; wherein gas generated within the battery housing during the retaining step and pre-charging step is vented out of the battery housing through the at least one hole.

[0092] The method may include the step of retaining the electrolyte within the battery housing (“aging”) for a period of at least 5 minutes after the step of adding an electrolyte to the battery housing and before the step of applying charge across the pair of electrodes. The step of retaining the electrolyte in the battery housing may allow the electrolyte to penetrate through the battery housing to the electrodes. The step of retaining the electrolyte in the battery housing may allow the electrolyte to penetrate through the electrodes.

[0093] The step of retaining the electrolyte in the battery housing may be for a period of at least 10 minutes. The step of retaining the electrolyte in the battery housing may be for a period of at least 20 minutes. The step of retaining the electrolyte in the battery housing may be for a period of at least 30 minutes.

[0094] The step of retaining the electrolyte in the battery housing may be for a period of from 5 minutes to three hours. The step of retaining the electrolyte in the battery housing may be for a period of from 10 minutes to three hours. The step of retaining the electrolyte in the battery housing may be for a period of from 20 minutes to three hours. The step of retaining the electrolyte in the battery housing may be for a period of from 30 minutes to three hours. The step of retaining the electrolyte in the battery housing may be for a period of from 40 minutes to three hours. The step of retaining the electrolyte in the battery housing may be for a period of from 50 minutes to three hours. The step of retaining the electrolyte in the battery housing may be for a period of from one hour to three hours. The step of retaining the electrolyte in the battery housing may be for a period of from 5 minutes to two and a half hours. The step of retaining the electrolyte in the battery housing may be for a period of from 5 minutes to two hours. The step of retaining the electrolyte in the battery housing may be for a period of from 5 minutes to one and a half hours. The step of retaining the electrolyte in the battery housing may be for a period of from 5 minutes to one hour.

[0095] The battery housing may comprise an electrolyte inlet and the electrolyte may be added to the battery housing through the electrolyte inlet. The electrolyte inlet may be sealed after the electrolyte has been added. The step of adding electrolyte into the battery housing may be carried out under vacuum conditions. The step of adding electrolyte into the battery housing may be carried out under dry conditions. Accordingly, interior of the battery housing may be protected from liquid water and water vapour during the step of adding electrolyte to the battery housing.

[0096] The step of retaining the electrolyte within the battery housing may be carried out in normal conditions (i.e. not under dry conditions or vacuum conditions). The formation vent may protect the interior of the battery housing from the ingress of liquid water, water vapour and other contaminants such that dry or vacuum conditions are not required.

[0097] The step of retaining the electrolyte within the battery housing may allow the battery as a whole to reach equilibrium or approach equilibrium.

[0098] The method may further comprise the step of allowing the charged battery to rest or age after the step of pre-charging the battery.

[0099] The formation vent may be a venting element of the first aspect. Accordingly, features of the venting element of the first aspect may be features of the formation vent of the third aspect.

[0100] The at least one hole may extend from a first side of the non-permeable substrate to a second side of the non-permeable substrate and the maximum width of the at least one hole on the first side of the non-permeable substrate may be at least 30% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate.

[0101] The first side of the non-permeable substrate may face away from the battery housing. The first side of the non-permeable substrate may face into the battery housing. In embodiments where the maximum width of the at least one hole on the first side of the non-permeable substrate is at least 30% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate the first side of the non-permeable substrate may face into the battery housing such that the side of the hole with the smaller maximum width faces out of the battery housing.

[0102] The step of pre-charging the battery may be carried out until the battery holds at least 10 Ah. The step of pre-charging the battery may be carried out until the battery holds at least 20 Ah. The step of pre-charging the battery may be carried out until the battery holds at least 50 Ah. The step of pre-charging the battery may be carried out until the battery holds at least 100 Ah. The step of pre-charging the battery may be carried out until the battery holds at least 150 Ah. The step of pre-charging the battery may be carried out until the battery holds at least 200 Ah. The step of pre-charging the battery may be carried out until the battery holds from 10 Ah to 500 Ah. The step of pre-charging the battery may be carried out until the battery holds from 10 Ah to 250 Ah. The step of pre-charging the battery may be carried out until the battery holds from 10 Ah to 200 Ah. The step of pre-charging the battery may be carried out until the battery holds from 10 Ah to 1500 Ah. The step of pre-charging the battery may be carried out until the battery holds from 10 Ah to 100 Ah. The step of pre-charging the battery may be carried out until the battery holds from 50 Ah to 500 Ah. The step of pre-charging the battery may be carried out until the battery holds from 100 Ah to 500 Ah. The step of pre-charging the battery may be carried out until the battery holds from 150 Ah to 500 Ah.

[0103] The method may comprise the step of sealing the formation vent after the pre-charging step. The step of sealing the formation vent may include covering the formation vent with a sealing non-permeable substrate and fixing that sealing non-permeable substrate over the formation vent. The sealing non-permeable substrate may be configured to prevent the flow if gas across the formation vent. The step of sealing the formation vent may include applying conditions to the formation vent to close the at least one hole. In embodiments where the formation vent comprises a first protective element on the outside of the battery housing the step of sealing the formation vent may include applying conditions to the first protective element to occlude the at least one hole of the formation vent. For example, the step of sealing the formation vent may include applying a laser to the formation vent or the first protective element to ablate or weld the at least one hole or the material of the first protective element over the at least one hole to thereby block or otherwise close or occlude the at least one hole.

[0104] Gas generated during the step of applying charge across the pair of electrodes may be vented from within the battery housing through the at least one hole continuously.

[0105] The battery housing may comprise a venting element of the first aspect, the venting element spanning an aperture defined by the battery housing. Accordingly, the venting element may correspond to the formation vent.

[0106] The battery may be a battery prismatic cell and the battery housing may comprise a nonflexible prismatic wall.

[0107] The battery may be a battery pouch cell and the battery housing may comprise a flexible pouch wall. The battery housing may comprise a battery portion and a vent portion, the battery portion comprising the pair of electrodes and the vent portion comprising the at least one hole, and the method may further comprise the steps: sealing the battery portion from the vent portion; and separating the vent portion from the battery portion, wherein the remaining battery portion corresponds to a battery.

[0108] The step of sealing the battery portion from the vent portion may comprise forming a heat seal between the battery portion and the vent portion. The heat seal may adhere the inner wall of a first side of the flexible pouch wall to the inner wall of an opposed second side of the flexible pouch wall. The heat seal may fuse the inner wall of a first side of the flexible pouch wall to the inner wall of an opposed second side of the flexible pouch wall. The heat seal may extend along the entirety of the flexible pouch wall to fully separate the battery portion from the vent portion.

[0109] The vent portion may comprise a gas absorbent. The gas absorbent may be configured to absorb gas generated during the step of applying charge across the pair of electrodes. The gas absorbent may be provided in an absorbent retainer. The absorbent retainer may separate the gas absorbent from the electrolyte of the battery portion. The absorbent retainer may comprise a retainer wall. The retainer wall may comprise the same or similar materials to that of the housing wall. The retainer wall may comprise at least one polymer. The retainer wall may comprise at least one polymer. The at least one polymer may comprise a fluoropolymer such as PTFE, PFA, FEP or copolymers thereof. The at least one polymer may comprise a non-fluoropolymer such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) or copolymers thereof. The retainer wall may comprise a combination of at least one metal layer and at least one polymer layer. The retainer wall may comprise at least one metal layer provided in between at least two polymer layers.

[0110] The retainer wall may comprise the at least one hole. Accordingly, gas generated during the step of applying charge across the pair of electrodes may pass from the electrolyte into the absorbent retainer via the at least one hole.

[0111] The retainer wall may be permeable to gas generated during the step of applying charge across the pair of electrodes such that gas may pass through the retainer wall from the vent portion to be absorbed by the gas absorbent. The absorbent retainer may share a wall with the vent portion. Shared wall may comprise the at least one hole, such that gas from the absorbent retainer may be vented through the at least one hole to the exterior of the vent portion.

[0112] The gas absorbent may comprise any material that is configured to absorb or adsorb gas generated during the step of applying charge across the pair of electrodes. For example, the gas absorbent may comprise activated carbon. The gas absorbent may comprise a zeolite. The zeolite may be selected from the following types of zeolite: A-type zeolite, L-type zeolite, P-type zeolite, MFI-type zeolite, or faujasite-type zeolite. In some embodiments the zeolite may be a MFI-type zeolite selected from ZSM-5 type zeolite or ZSM-11 type zeolite. The gas absorbent may comprise carbon black, metals, metal oxides, metal nitrides, or intermetallic compounds.

[0113] In a fourth aspect there is provided a method of preparing a battery, the method comprising the steps: providing a battery housing comprising an aperture defined in a housing wall, and a pair of electrodes; adding a first amount of electrolyte through the aperture to the battery housing; installing a formation vent into the battery housing such that the formation vent occludes the aperture; and applying charge across the pair of electrodes to thereby pre-charge the battery; wherein gas generated in the battery housing during pre-charging step is vented out of the battery housing through the at least one hole.

[0114] The method may comprise the step of retaining the electrolyte within the battery housing for a period of at least 5 minutes. The step of retaining the electrolyte within the battery housing may be carried out before the step of applying charge across the pair of electrodes.

[0115] The formation vent may be removed after the step of pre-charging the battery.

[0116] The method may comprise the step of adding a second amount of electrolyte to the battery housing through the aperture after the formation vent has been removed.

[0117] The method may comprise the step of sealing the aperture after the step of removing the formation vent or after the step of adding a second amount of electrolyte to the battery housing. The steps of adding a first amount of electrolyte to the battery housing through the aperture and, where present, of adding a second amount of electrolyte to the battery housing through the aperture may be carried out in dry conditions.

[0118] The step of charging the battery may be carried out outside of dry conditions due to the formation vent protecting the interior of the battery housing from the ingress of liquid water, water vapour or other contaminants.

[0119] The step of sealing the aperture may include covering the aperture with a sealing non- permeable substrate and fixing that sealing non-permeable substrate over the aperture. The sealing non-permeable substrate may be configured to prevent the flow if gas across the aperture. The step of sealing the aperture may include applying conditions to the aperture to close the aperture. For example, the step of sealing the aperture may include applying a laser to the aperture to ablate or weld the aperture to thereby block or otherwise close or occlude the aperture.

[0120] Brief Description of the Figures

[0121] Embodiments of the present invention will now be described, by way of non-limiting example, with reference to the accompanying drawings.

[0122] Figure 1 : A schematic side view of a test set up for measuring CO2 transmission rate;

[0123] Figure 2: A schematic side view of a test set up for measuring water vapour transmission rate; Figure 3: A schematic method of preparing a prismatic cell (<100Ah cell) known in the art;

[0124] Figure 4: A schematic method of preparing a prismatic cell (>100Ah cell) known in the art;

[0125] Figure 5: A schematic method of preparing a pouch battery cell known in the art;

[0126] Figure 6: A prismatic battery cell according to an embodiment;

[0127] Figure 7: A schematic side view of a venting element mounted over an aperture defined in a battery housing wall;

[0128] Figure 8: A schematic method of preparing a prismatic cell according to an embodiment;

[0129] Figure 9: A pouch battery cell according to an embodiment;

[0130] Figure 10: A schematic method of preparing a pouch battery cell according to an embodiment; Figure 11 : A pouch battery cell housing to be made into a pouch battery cell using a method according to an embodiment;

[0131] Figure 12: A pouch battery cell and a separated gas portion that has been removed from the pouch battery cell housing of Figure 11 during a method according to an embodiment;

[0132] Figure 13: A schematic method of preparing a pouch battery cell according to an embodiment; Figure 14: An SEM of a conical hole formed in a non-permeable substrate A) on a first side of the non-permeable substrate and B) on a second side of the nun-permeable substrate;

[0133] Figure 15: A schematic side view of a conical hole extending through a non-permeable substrate;

[0134] Figure 16: A scanned electron micrograph (SEM) of a hole formed in a non-permeable substrate;

[0135] Figure 17: A schematic side view of a cylindrical hole extending through a non-permeable substrate;

[0136] Figure 18: A plot of gas flow rate as a function of hole size for straight and tapered holes;

[0137] Figure 19: A plot of gas flow rate as a function of hole size for straight and tapered holes;

[0138] Figure 20: A plot of gas flow rate as a function of substrate thickness to hole maximum width aspect ratio;

[0139] Figure 21 : A plot of gas flow rate as a function of substrate thickness to hole maximum width aspect ratio;

[0140] Figure 22: A plot of CO2 transmission rate to water vapour transmission rate ratio as a function of hole size;

[0141] Figure 23: A plot of CO2 transmission rate to water vapour transmission rate ratio as a function of hole size;

[0142] Figure 24: A plot of CO2 transmission rate to water vapour transmission rate ratio as a function of substrate thickness to hole maximum width aspect ratio;

[0143] Figure 25: A plot of CO2 transmission rate to water vapour transmission rate ratio as a function of substrate thickness to hole maximum width aspect ratio;

[0144] Figure 26: A pouch battery cell housing to be made into a pouch battery cell using a method according to an embodiment;

[0145] Figure 27: A pouch battery cell and a separated gas portion that has been removed from the pouch battery cell housing of Figure 11 during a method according to an embodiment; and Figure 28: A schematic method of preparing a pouch battery cell according to an embodiment.

[0146] Detailed Description

[0147] 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.

[0148] 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.

[0149] Test Methods

[0150] CO2 transmission rate

[0151] Determination of the CO2 transmission rate through a substrate was carried out in accordance with ASTM D1434-82 (Standard Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting). The differential pressure test method was used. The test setup was shown in Figure 1.

[0152] For samples with relatively high CO2 transmission rate of more than 3,000,000 cm3 / (m2day bar), a Gas Permeability Analyzer GTR series by GTR Tec Corporation, Japan (model# GTR-11MJGG) using a Shimadzu GC-2014 gas chromatograph was used to measure the gas transmission rate of the substrate. A sample substrate was placed on an aluminum mask holder with a 15.2 cm2opening in the center. The mask was cut to approximately 6 x 6 cm. It was then affixed inside an instrument testing cell and sealed in a chamber. Vacuum was applied for 10 min to remove air in the testing chamber. Dry CO2 gas was then introduced into the chamber on a first side of the substrate. A differential pressure across the substrate of 99 kPa was conditioned for the measurement. The CO2 that passes into the second side of the substrate through the sample substrate was detected to provide the transmission rate for that substrate. The test temperature was set at 30 °C. Analyte collection time set at 5 to 10 s and GC analysis time was set at 10 min. CO2 transmission rate was reported by the instrument in the unit cm3 / (m2day atm). It was converted to the unit of cm3.cm / (cm2.s.bar) where values of volume are at standard temperature and pressure as defined above.

[0153] Moisture transmission rate

[0154] Determination of the water vapor permeability through a substrate was carried out in accordance with ASTM F 1249-20 (Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor). The equal pressure method was used. The test setup was shown in Figure 2. Specifically, the instrument used to test the water vapor transmission rate of the materials was a Water Vapor Permeation Analyzer by Lyssy (model L-80 type). A sample substrate was placed on an aluminum mask holder with a 5 cm2opening in the center. The mask was then affixed to an instrument testing cell and sealed in a chamber. A sample substrate was provided to split a sample chamber into a first portion (high humidity chamber) and a second portion (low humidity chamber). The first portion retains water to create a high humidity side of the sample substrate. Dry nitrogen gas was passed through the second side to provide a low humidity side of the sample substrate. Both the first portion and the second portion of the chamber are maintained at ambient pressure. The test was performed at 90% Relative Humidity at 40 °C on the high humidity side. The water vapor that passes from the first side of the substrate on the high humidity side into the second side of the substrate on the low humidity side through the sample substrate in the “dry gas” outlet was detected to thereby measure the water vapor that has passed through the sample substrate. Water vapor transmission rate was reported by the instrument in the unit of g / (m2day).

[0155] Water vapor transmission rate was converted to the unit of cm3.cm / (cm2.s.bar) using the ideal gas law and dividing by the partial water vapor pressure differential (0.066 bar) where volume was converted to that for standard temperature and pressure as defined above. Both carbon dioxide (CO2) transmission rate and water vapor (moisture) transmission rate in the unit of cm3.cm / (cm2.s.bar) where volume was converted to that for standard temperature and pressure as defined above were used to calculate carbon dioxide (CO2) transmission rate to water vapor (moisture) transmission rate ratio by dividing the CO2 transmission rate by the water vapor transmission rate. CO2 transmission to water vapor transmission ratio has no units (i.e., is dimensionless).

[0156] Image analysis is used to calculate the surface area of the hole from an SEM image. The effective diameter of the hole is calculated from the measured area of the hole on the laser exit side. Image analysis is used to estimate the maximum width of the hole from an SEM image.

[0157] Substrate thickness of polymer films was measured using a Mitutoyo Litematic VL50S thickness gauge. Substrate thickness of Aluminum foils was measured using a Mitutoyo 547- 400S Digimatic thickness gauge.

[0158] Batteries that comprise a prismatic-type battery housing or a pouch-type battery housing are typically prepared by assembling the battery housing in a first step. Once the battery housing has been assembled it is necessary to add electrolyte, charge the battery and to seal the battery housing before the battery is ready to be shipped to customers. With reference to Figure 3, medium sized batteries made of a prismatic can battery housing (“a prismatic cell”) and designed to retain a charge of less than 100 Amp hours (<100Ah) are often made using the following process 1 whilst the battery housing is maintained in dry conditions.

[0159] An electrolyte is injected 2 into the battery housing through an aperture formed in the battery housing. Once the electrolyte has been injected, the battery is allowed to age 4 for a period of time. A charge is then applied 6 across the electrodes of the battery to pre-charge the battery 6. As charge is applied across the electrodes gas is often generated within the battery housing and is vented through the aperture. Once the battery has been charged the battery is aged for a further period of time 8 before the aperture is then sealed and the battery is ready to be shipped.

[0160] The entirety of the process must be carried out in dry conditions to ensure that water does not enter the battery housing and therefore the process is often carried out in a dry room that has been specifically adapted and which involves additional costs and complications.

[0161] With reference to Figure 4, large batteries made of a prismatic can battery housing (“a prismatic cell”) and designed to retain a charge more than 100 Ah (>100Ah) are often made using the following process 20, again whilst the battery housing is maintained in dry conditions.

[0162] An electrolyte is injected 22 into the battery housing through an aperture formed in the battery housing. The aperture is then plugged 24 with a rubber plug and the battery is allowed to rest for a period of time. A charge is then applied across the electrodes of the battery to pre-charge 26 the battery. As gas is generated within the battery housing the pressure within the battery housing increases. The rubber plug is then removed 28 and gas generated within the battery housing during the pre-charge step 26 is vented 30 from the battery housing under vacuum. In addition, due to the increase of pressure electrolyte often spills out from within the battery housing through the aperture. As a result, further electrolyte is injected 32 into the battery housing to replace the spilled electrolyte and the aperture is then sealed before the battery is ready to be shipped.

[0163] The entirety of the process must be carried out in dry conditions to ensure that water does not enter the battery housing and therefore the process is often carried out in a dry room that has been specifically adapted and which involves additional costs and complications. A pouch cell battery typically comprises a flexible housing that is made of a laminate material. The laminate material often comprises a polypropylene (PP) layer, an aluminium (Al) foil layer and a polyethylene terephthalate (PET) / nylon (NL) layer. The PP layer is provided on the inside of the pouch cell and the PET / NL layer is provided on the outside of the pouch cell with the Al layer provided in between.

[0164] Pouch cell batteries are often made using the following process 40 (see Figure 5). The flexible housing comprises a gas vent portion and a body portion.

[0165] An electrolyte is injected 42 into the flexible housing through an aperture in the flexible housing that is then sealed. The flexible housing is then aged for a period of time 44 before a charge is applied 46 across the electrodes of the flexible housing. As charge is applied gas is often generated within the flexible housing to thereby increase the internal pressure of the flexible housing. Accordingly, in order to relieve the increased pressure, the gas vent portion of the flexible housing is pierced 48 and the gas is thereby allowed to escape under vacuum. The gas vent portion is then sealed 50 from the body portion and the gas vent portion then removed 52.

[0166] The initial step 42 of injecting electrolyte into the flexible housing must be carried out under dry conditions, and the step 48 of piercing the gas vent portion and sealing 50 are carried out under vacuum. These stringent conditions add to the cost of the process. Further, the removal of the gas vent portion requires the initial flexible housing to be significantly larger than is required for the pouch cell battery to be made.

[0167] Example 1

[0168] With reference to Figure 6 and Figure 7 a prismatic cell battery 80 comprises a battery housing 86, a pair of electrodes 82, an electrolyte aperture 84 and a formation vent 88, 160 (acting as a venting element). The formation vent 88, 160 comprises an aluminium substrate 164 and a protective element 168 (acting as a first protective element). A vent hole (acting as an at least one hole) 166 is formed through the aluminium substrate 164 and is covered by the protective element 168. The formation vent 88, 160 spans an aperture 170 defined within the battery housing 86 and occludes that aperture 170.

[0169] A method 60 of preparing a prismatic cell battery 80 is generally shown in Figure 8. Electrolyte is injected 62 into the prismatic cell battery 80 through the electrolyte aperture 84. The electrolyte aperture 84 is then sealed 64. The prismatic cell battery 80 then rests or ages 66 for a period of time before a charge is applied across the pair of electrodes 82 in a pre-charge step 68 and any gas generated within the battery housing 86 during the pre-charge step 68 is vented through the formation vent 88, 160 continuously such that there is no substantial pressure increase within the battery housing 86. The prismatic cell battery 80 is then allowed to rest or age 70 before the formation vent 88, 160 is sealed and the prismatic cell battery 80 is ready to ship.

[0170] The formation vent 88, 160 protects the interior of the battery housing 86 from exterior contaminates such as water vapor or particulates and so once the electrolyte aperture 84 is sealed 64 the prismatic cell battery may be prepared outside of strict dry conditions. Accordingly, the prismatic cell battery only requires stringent dry conditions during the step of electrolyte injection 62, significantly simplifying the process, thereby reducing the cost of preparation.

[0171] Example 2

[0172] A pouch cell battery 90 (Figure 9) comprises a flexible housing 94, a pair of electrodes 92 and a formation vent 96 (acting as a venting element). The flexible housing 94 is a laminate of a PP layer, an aluminium foil layer and a PET layer. The PP layer is provided on the interior of the flexible housing 94 and the PET layer is provided on the exterior of the flexible housing 94. The flexible housing 94 defines a vent aperture (not shown) and the formation vent 96 spans the vent aperture. The formation vent 96 comprises an aluminium substrate, a first protective layer provided on a first side of the aluminium substrate and a second protective layer provided on a second side of the aluminium substrate, the second side opposed to the first side.

[0173] A method 100 of preparing a pouch cell battery 90 is generally shown in Figure 10. Electrolyte is injected 102 into the pouch cell battery 90 through an electrolyte aperture (not shown). The electrolyte aperture is then sealed. The pouch cell battery 90 then rests or ages 104 for a period of time before a charge is applied across the pair of electrodes 92 in a pre-charge step 106 and any gas generated within the flexible housing 94 during the pre-charge step 106 is vented through the formation vent 96 continuously such that there is no substantial pressure increase within the flexible housing 94. The formation vent 96 is then sealed and the pouch cell battery 90 is ready to ship.

[0174] The formation vent 96 protects the interior of the flexible housing 94 from exterior contaminates such as water vapor or particulates and so once the electrolyte aperture 84 is sealed 64 the pouch cell battery 90 may be prepared outside of strict dry conditions. Furthermore, the provision of the formation vent 96 in the flexible housing 94 means that there is no need to provide a gas portion of the flexible housing 94 that is pierced to allow gas generated within the flexible housing 94 to be vented. Accordingly, the amount of laminate material used to form the flexible housing is significantly reduced and the risk of electrolyte spillage during venting is completely removed.

[0175] Example 3

[0176] A pouch cell battery 120 (Figure 11 and Figure 12) comprises a flexible housing 124, a pair of electrodes 122 and a formation vent 130 (acting as a venting element). The flexible housing 124 is a laminate of a PP layer, an aluminium foil layer and a PET layer. The PP layer is provided on the interior of the flexible housing 124 and the PET layer is provided on the exterior of the flexible housing 124. The flexible housing 124 comprises a body portion 126 and a gas portion 128 (acting as a vent portion). The flexible housing defines a vent aperture (not shown) in the gas portion 128 and the formation vent 130 spans the vent aperture. The formation vent 96 comprises an aluminium substrate, a first protective layer provided on a first side of the aluminium substrate and a second protective layer provided on a second side of the aluminium substrate, the second side opposed to the first side.

[0177] A method 140 of preparing a pouch cell battery 120 is generally shown in Figure 13. Electrolyte is injected 142 into the pouch cell battery 120 through an electrolyte aperture (not shown). The electrolyte aperture is then sealed. The pouch cell battery 120 then rests or ages 144 for a period of time before a charge is applied across the pair of electrodes 122 in a pre-charge step 146 and any gas generated within the flexible housing 124 during the precharge step 146 is vented through the formation vent 130 continuously such that there is no substantial pressure increase within the flexible housing 124. A heat seal is then formed 148 between the gas portion 128 and the body portion 126 to thereby seal the body portion 126 from the gas portion 128. The gas portion 128 is then cut from the body portion 126 such that the electrolyte within the body portion 126 remains sealed within the body portion 126.

[0178] The provision of the formation vent 130 in the gas portion 128 allows the existing process for forming a pouch cell battery (such as described above with reference to Figure 5, for example) without requiring piercing of the gas portion and therefore prevents spillage of electrolyte and does not require the pouch cell battery to be under vacuum conditions during this step. Accordingly, the provided method reduces the required stringent conditions for preparation of a pouch cell battery, thereby reducing the incurred costs.

[0179] Example 4 A formation vent (acting as a venting element), a cross-section portion of which is shown in Figure 15, and SEM images of the first side and the second side in Figure 14 comprises a polytetrafluoroethylene (PTFE) substrate having a thickness 180 and a hole (acting as an at least one hole) laser drilled from a first side 174 to a second side 178. The hole has a first maximum width 172 on the first side 174 of the substrate and a second maximum width 176 on the second side 178 of the substrate. The first maximum width 172 is larger than the second maximum width 176 and the hole tapers from the first side 174 to the second side 176.

[0180] A further formation vent (acting as a venting element), a cross-section portion of which is shown in Figure 17 and the first side of the substrate in Figure 16, comprises a PTFE substrate having a thickness 198 and a hole (acting as an at least one hole) laser drilled from a first side 192 to a second side 196. The hole has a first maximum width 190 on the first side 192 of the substrate and a second maximum width 194 on the second side 196 of the substrate. The first maximum width 190 is the same as the second maximum width 194 within measurement tolerances and the hole is approximately cylindrical from the first side 192 to the second side 196.

[0181] It has been found that a venting element comprising a tapered hole (or a conical hole) can provide improved resistance to water vapor transmission (i.e. has a reduced water vapour transmission rate) when compared to a linear or cylindrical hole. In particular, a venting element comprising a tapered hole that is oriented such that the side of the hole that has the smallest maximum width is the side to which water vapour is incident provides further reduced water vapour transmission. Gas flow rate as a function of hole size is shown in Figure 18 and Figure 19. Gas flow as a function of substrate to hole size aspect ratio is shown in Figure 20 and Figure 21. The CO2 transmission rate to water vapour transmission rate ratio (CO2 / H2O ratio) for a variety of hole sizes for straight and tapered holes are shown in Figures 22 and 23 and it is clearly shown that tapered holes have an improved ratio compared to straight holes.

[0182] In addition, Figures 24 and 25 show the CO2 / H2O ratio as a function of substrate thickness to hole maximum width aspect ratio. As can be seen, the CO2 / H2O ratio is significantly increased for tapered holes compared to straight holes.

[0183] Examples 5 to 12

[0184] Further specific examples of venting elements are provided in Table 1 below comprising a 100 pm thick aluminium substrate with a single hole that has been laser-drilled through the substrate. Examples 5 to 8 are straight holes with a cylindrical shape and having the same maximum width on both sides of the substrate (HS1 = HS2). Examples 9 to 12 are tapered with a conical shape and the maximum width on the first side of the substrate is greater than the maximum width on the second side of the substrate (HS1 > HS2). Table 1 : Example venting elements with straight and tapered laser-drilled holes.

[0185] The carbon dioxide transmission rate (“CO2 GTR”), indicative of the gas transmission rate, the moisture vapour transmission rate (“MVTR”), or water vapour transmission rate, and the ratio of the CO2 GTR to MVTR is provided below in Table 2 for each example as measured from the first side to the second side, and from the second side to the first side for Examples 9 to 12. Table 2: Gas transmission rates (“CO2 GTR”), water vapour transmission rates (“MVTR”) and gas to moisture transmission rate ratios (“CO2 / H2O “) for Examples 5 to 12. GTR and MVTR provided in units of cm3.cm / (cm2.s.bar).

[0186] Table 3: Gas transmission rates (“CO2 GTR”), water vapour transmission rates (“MVTR”) and gas to moisture transmission rate ratios (“CO2 / H2O “) for Examples 5 to 12.

[0187] As can be seen, all examples have good CO2 to water vapour transmission rate ratios (greater than 15). Furthermore, the ratio of CO2 to water vapour transmission is significantly increased for Examples 9 to 12 when measured from the second side (having the smaller hole maximum width) to the first side (having the larger hole maximum width).

[0188] Accordingly, the venting elements described herein are particularly useful for methods of protecting the interior of a battery housing during the preparation of batteries to allow gas generated within the battery housing to be safely and efficiently vented out of the battery housing whilst also effectively preventing the ingress of water vapour into the battery housing interior.

[0189] Example 13

[0190] A pouch cell battery 200 (Figure 26 and Figure 27) comprises a flexible housing 202, a pair of electrodes 204. The flexible housing 202 is a laminate of a PP layer, an aluminium foil layer and a PET layer. The PP layer is provided on the interior of the flexible housing 202 and the PET layer is provided on the exterior of the flexible housing 202. The flexible housing 202 comprises a body portion 206 and a gas portion 208 (acting as a vent portion). The gas portion 208 comprises an absorbent retainer 210. The absorbent retainer 210 comprises a retainer wall 212 and retains a zeolite (acting as a gas absorbent). The retainer wall 212 comprises a formation vent 214 (acting as a venting element). The retainer wall 212 defines a vent aperture (not shown) absorbent retainer 210 and the formation vent 214 spans the vent aperture. The formation vent 214 comprises an aluminium substrate, a first protective layer provided on a first side of the aluminium substrate and a second protective layer provided on a second side of the aluminium substrate, the second side opposed to the first side.

[0191] A method 220 of preparing a pouch cell battery 200 is generally shown in Figure 28. Electrolyte is injected 222 into the pouch cell battery 200 through an electrolyte aperture (not shown). The electrolyte aperture is then sealed. The pouch cell battery 200 then rests or ages 224 for a period of time before a charge is applied across the pair of electrodes 204 in a pre-charge step 226 and any gas generated within the flexible housing 202 during the precharge step 226 is vented through the formation vent 214 continuously into the absorbent retainer 210 where it is absorbed by the zeolite such that there is no substantial pressure increase within the flexible housing 202. A heat seal is then formed 228 between the gas portion 208 and the body portion 206 to thereby seal the body portion 206 from the gas portion 208. The gas portion 208 is then cut 230 from the body portion 206 such that the electrolyte within the body portion 206 remains sealed within the body portion 206.

[0192] The provision of the formation vent 214 in the gas portion 208 allows the existing process for forming a pouch cell battery (such as described above with reference to Figure 5, for example) without requiring piercing of the gas portion and therefore prevents spillage of electrolyte and does not require the pouch cell battery to be under vacuum conditions during this step. Accordingly, the provided method reduces the required stringent conditions for preparation of a pouch cell battery, thereby reducing the incurred costs.

[0193] Whilst the above methods, batteries and venting elements described above are discussed in reference to battery capacities of less than 100Ah (<100Ah) and more than 100 Ah (>100Ah), it will be appreciated that they appropriate for battery capacities of any size that are applicable in the mobile electronic device and automotive applications.

[0194] 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.

Claims

Claims1. A venting element comprising a non-permeable substrate, and a first protective element , the non-permeable substrate comprising at least one hole, the or each hole extending from a first side of the non-permeable substrate to a second side of the non- permeable substrate and the or each hole has a maximum width of from 1 pm to 50 pm, the first protective element being positioned on the first side of the non-permeable substrate occluding the or each holes.

2. The venting element of claim 1 , wherein the or each hole has a maximum width of from 10 pm to 30 pm.

3. The venting element of claim 1 or claim 2, wherein the first protective element comprises an expanded polymer selected from expanded polytetrafluoroethylene and expanded polyethylene.

4. The venting element of and preceding claim, wherein the venting element comprises a second protective element being positioned on the second side of the non-permeable substrate occluding the or each hole.

5. The venting element of any preceding claim, wherein each of the first protective element and the second protective element where present have a higher CO2 transmission rate than the or each hole.

6. The venting element of any preceding claim, wherein each of the first protective element, and the second protective element where present, have an airflow of at least 20 ml / h.

7. The venting element of any preceding claim, wherein the CO2 transmission rate through the venting element is at least 10 ml / hour.

8. The venting element of any preceding claim, wherein the water vapor transmission rate through the venting element is less than 1.0 mg / h.

9. The venting element of any preceding claim, wherein the CO2 transmission rate to water vapor transmission rate through the venting element is at least 5.

10. The venting element of any preceding claim, wherein the CO2 transmission rate to water vapor transmission rate through the venting element is from 5 to 2000.

11. The venting element of any preceding claim, wherein the at least one hole is approximately conical and the maximum width on the first side of the non-permeable substrate is different to the maximum width on the second side of the non-permeable substrate.

12. The venting element of claim 11 , wherein the maximum width of the at least one hole on the first side of the non-permeable substrate is at least 30% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate.

13. The venting element of claim 11 , wherein the maximum width of the at least one hole on the first side of the non-permeable substrate is at least 30% smaller than the maximum width of the at least one hole on the second side of the non-permeable substrate.

14. The venting element of any of claim 11 to claim 13, wherein the at least one hole has a first end adjacent to the first side of the non-permeable substrate and a second end adjacent to the second side of the non-permeable substrate, the first end having a first maximum width and the second end having a second maximum width, wherein the first maximum width is larger than the second maximum width and the CO2 to water vapour ratio from the second side of the non-permeable substrate to the first side of the non- permeable substrate of at least 2.

15. A battery comprising a housing wall, the housing wall comprising a non-permeable substrate and at least one hole provided in the non-permeable substrate, the or each hole extends from a first side of the non-permeable substrate to a second side of the non-permeable substrate and the or each hole has a maximum width of from 1 pm to 50 pm.

16. The battery of claim 15, wherein the battery is a battery pouch cell or a battery prismatic cell.

17. The battery of claim 15 or claim 16, wherein the housing wall comprises at least one of: a metal, a metal alloy, at least one polymer, or a combination thereof.

18. The battery of claim 17, wherein at least one polymer comprises a fluoropolymer such as PTFE, PFA, FEP or a non-fluoropolymer such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) or copolymers thereof.

19. The battery of any of claim 15 to claim 18, wherein the housing wall comprises at least one metallic layer and at least one polymer layer.

20. The battery of any of claim 15 to claim 19, wherein the housing wall comprises a vent aperture and the non-permeable substrate occludes the vent aperture.

21. The battery of any of claim 15 to claim 20, wherein the at least one hole is approximately conical and the maximum width on the first side of the non-permeable substrate is different to the maximum width on the second side of the non-permeable substrate.

22. The battery of claim 21 , wherein maximum width of the at least one hole on the first side of the non-permeable substrate is larger than the maximum width of the at least one hole on the second side of the non-permeable substrate.

23. The battery of claim 21 or claim 22, wherein the maximum width on the first side of the non-permeable substrate is at least 30% larger than the maximum width on the second side of the non-permeable substrate.

24. The battery of claim 22 or claim 23, wherein the first side of the non-permeable substrate faces away from the battery housing, or the first side of the non-permeable substrate faces into the battery housing.

25. The battery of any of claim 15 to claim 24, wherein the battery housing comprises at least one protective element provided on at least one of a first major surface and a second major surface of the non-permeable substrate and covers the or each hole.

26. The battery of claim 25, wherein the battery housing comprises two protective elements.

27. The battery of claim 26, wherein the two protective elements comprise a first protective element provided on the first major surface and a second protective element providedon the second major surface such that the or each hole is covered by the first protective element and the second protective element.

28. The battery of any of claim 15 to claim 27, wherein the at least one protective element comprises an expanded polymer.

29. The battery housing of claim 28, wherein the at least one protective element comprises expanded polytetrafluoroethylene (ePTFE) or expanded polyethylene (ePE).

30. The battery housing of any of claim 15 to claim 29, wherein the battery housing comprises a venting element of any of claim 1 to claim 14.31 . A method of preparing a battery, the method comprising the steps: providing a battery housing comprising a formation vent within a housing wall, and a pair of electrodes, the formation vent comprising a non-permeable substrate and at least one hole provided in the non-permeable substrate, the at least one hole having a maximum width of from 1 pm to 50 pm; adding an electrolyte to the battery housing to form a battery; and applying charge across the pair of electrodes to thereby pre-charge the battery; wherein gas generated within the battery housing during the retaining step and precharging step is vented out of the battery housing through the at least one hole.

32. The method of claim 31 , wherein the method comprises the step of retaining the electrolyte within the battery housing for a period of at least 5 minutes.

33. The method of claim 32, wherein the step of retaining the electrolyte in the battery housing is for a period of from 5 minutes to three hours.

34. The method of any of claim 31 or claim 33, wherein the formation vent has a carbon dioxide to water vapour ratio of at least 10.

35. The method of any of claim 31 to claim 34, wherein the formation vent has a carbon dioxide to water vapour ratio of from 10 to 2000.

36. The method of any of claim 31 to claim 35, wherein the at least one hole has a maximum width of from 1 to 40 pm.

37. The method of claim 36, wherein the at least one hole has a maximum width of from 10 to 30 pm.

38. The method of any of claim 31 to claim 37, wherein the at least one hole extends from a first side of the non-permeable substrate to a second side of the non-permeable substrate and the maximum width of the at least one hole on the first side of the non- permeable substrate is at least 30% larger than the maximum width of the at least one hole on the second side of the non-permeable substrate.

39. The method of claim 38, wherein the first side of the non-permeable substrate faces away from the battery housing.

40. The method of claim 39, wherein the first side of the non-permeable substrate faces into the battery housing.41 . The method of any of claim 31 to claim 40, wherein the method comprises the step of sealing the formation vent after the pre-charging step.

42. The method of any of claim 31 to claim 41 , wherein gas generated during the step of applying charge across the pair of electrodes is vented from within the battery housing through the at least one hole continuously.

43. The method of any of claim 31 to claim 42, wherein the battery housing comprises a vent element of any of claim 1 to claim 14, the venting element spanning an aperture defined by the battery housing.

44. The method of any of claim 31 to claim 43, wherein the battery is a battery pouch cell and the battery housing comprises a flexible pouch wall.

45. The method of claim 44, wherein the battery housing comprises a battery portion and a vent portion, the battery portion comprising the pair of electrodes and the vent portion comprising the at least one hole, and the method further comprises the steps: sealing the battery portion from the vent portion; andseparating the vent portion from the battery portion, wherein the remaining battery portion corresponds to a battery.

46. The method of claim 45, wherein the step of sealing the battery portion from the vent portion comprises forming a heat seal between the battery portion and the vent portion.

47. The method of claim 44 or claim 45, wherein the vent portion comprises a gas absorbent provided within an absorbent retainer, the gas absorbent being configured to absorb gas generated during the step of applying charge across the pair of electrodes.

48. The method of any of claim 31 to claim 43, wherein the battery is a battery prismatic cell and the battery housing comprises a non-flexible prismatic wall.

49. A method of preparing a battery, the method comprising the steps: providing a battery housing comprising an aperture defined in a housing wall, and a pair of electrodes; adding a first amount of electrolyte to the battery housing; installing a formation vent into the battery housing such that the formation vent occludes the aperture; and applying charge across the pair of electrodes to thereby pre-charge the battery; wherein gas generated in the battery housing during the retaining step and precharging step is vented out of the battery housing through the at least one hole.

50. The method of claim 49, wherein the method comprises the step of retaining the electrolyte within the battery housing for a period of at least 5 minutes before the step of applying charge across the pair of electrodes.51 . The method of claim 49 or claim 50, wherein the formation vent is removed after the step of pre-charging the battery.

52. The method of claim 51 , wherein the method comprises the step of adding a second amount of electrolyte to the battery housing after the formation vent has been removed.

53. The method of claim 51 or claim 52, wherein the method comprises the step of sealing the aperture after the step of removing the formation vent or after the step of adding a second amount of electrolyte to the battery housing.

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