Flexible electrochemical energy storage device

Abstract

A flexible electrochemical energy storage device comprises at least two separated electrodes (110,112; figure 1) and an electrolyte (120; figure 1) contained within a flexible casing (118; figure 1) h

Description

The invention relates to a flexible electrochemical energy storage device comprising at least two separated electrodes and an electrolyte contained within a flexible casing constructed from a multi-layer laminate. The multi-layer laminate includes a barrier layer comprising a semi-crystalline polymeric film and a water-impervious metallic or inorganic film and a dampening layer comprising a substantially amorphous, low Tg polymer which dampens sound produced when flexing the flexible casing. The invention also relates to a method of producing such a flexible electrochemical energy storage device, and a flexible article of manufacture comprising the flexible electrochemical energy storage device. Background of Invention Electrochemical energy storage devices, including primary and secondary batteries and capacitors, are produced in a wide range of configurations depending on the intended application. Such devices commonly include a hard casing, usually made of metal, to retain the electrolyte and to exclude oxygen and moisture which can impair device performance. Hard casings typically contribute substantially to the device weight and define a rigid configuration for the electrochemical energy storage device as a whole. For some applications, however, an electrochemical energy storage device should be flexible, for example to allow the device to fit into differently shaped cavities or to flexibly adapt its configuration to accommodate movement. One such application is in garments or other wearable devices with integrated electronics or power systems designed to operate portable equipment. A flexible, low weight and relatively flat (planar) configuration is preferred because the electrochemical storage device can then conveniently be integrated into the fabric of a garment without causing discomfort or restricting the movement of the wearer. Other applications of interest include portable electronic devices such as medical monitoring devices. Flexible batteries suitable for garment applications have previously been reported. For example, US patent 8,192,863 discloses a lithium ion battery with an ionic liquid electrolyte and flexible electrodes, comprising cathode and anode materials supported on conductive fabric current collectors, retained within a flexible pouchtype casing. The flexible casing plays an important role in determining both the physical characteristics and the electrochemical cycling performance of a flexible electrochemical energy storage device. While it is desirable for the casing to be as light-weight and flexible as possible, these imperatives must be balanced against the requirements to hermetically seal the device against contaminants such as water vapour, to retain and resist chemical degradation by the electrolyte, and to maintain mechanical integrity when subjected to flexing in use. Flexible casing materials previously used in flexible battery applications include laminates of metal foils (typically aluminium) and adhesive polymer interlayers. The unsupported metal foils used as the barrier layer(s) in such laminates are relatively thick (typically greater than about 10 pm), thus providing excellent barrier properties while pristine. However, such metal foils restrict the flexibility of the laminate, so that the casing can become unacceptably stiffer than the fabric of a garment into which the electrochemical energy storage device is integrated. Moreover, metal foils are susceptible to permanent creasing and cracking when the casing is flexed in use, leading to failure and ingress of contaminants such as water. Another approach, described for example in US patent 5,326,652, uses a barrier layer in the form of a flexible polymeric film coated with a thin inorganic barrier coating. The flexible polymeric film provides the laminate casing structure with the necessary mechanical properties, including toughness and flexibility. The thin and flexible barrier coating, typically a metal, oxide or nitride coating deposited by vapour deposition techniques, is the primary contributor to the barrier properties, complemented by the flexible polymeric film which resists water permeation when semi-crystalline. This arrangement provides improved flexibility and / or durability relative to foil laminate structures while maintaining barrier properties which are acceptable for many applications. Thus, for example, laminates comprising one or more metallised semi-crystalline polymeric films (e.g. aluminised biaxially-oriented polyethylene terephthalate film) as the barrier layer(s) have previously been used to fabricate casings for flexible electrochemical energy storage devices. Despite advances to date, many laminates currently available for flexible battery casings are still insufficiently flexible. It would be desirable to produce casings for flexible electrochemical energy storage devices which have drape characteristics more compatible with textiles used in garment manufacture. A further significant shortcoming of many flexible electrochemical energy storage devices is the noise produced when the flexible casing is flexed in use. The inventors have found, in particular, that laminate casing materials which include a semi-crystalline flexible polymeric film in the barrier layer produce a crackling noise when subjected to twisting or crumpling movements. This is undesirable in many applications including energy storage devices integrated into garments. There is therefore an ongoing need for new flexible electrochemical energy storage devices which at least partially address one or more of the above-mentioned short-comings, or provide a useful alternative. A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims. Summary of Invention It has now been found that the addition of a substantially amorphous, low Tg polymer as a layer of a flexible casing laminate is surprisingly effective to dampen the sound produced when the laminate is flexed. Without wishing to be bound by any theory, the inventors attribute the crackling sounds produced in the absence of this layer to movement of the semi-crystalline polymeric film in the barrier layer, and propose that the substantially amorphous, low Tg polymer acts as a massdampening layer which dampens sound-producing motions of the semi-crystalline polymeric film and absorbs noises which are emitted. Furthermore, we have found that the outer layer of substantially amorphous, low Tg polymer can improve the flexibility of the laminate structure, imparting drape characteristics more compatible with fabrics suitable for garments or other flexible articles of manufacture. These advantages, which can be obtained without compromising the barrier properties or unacceptably increasing the thickness or mass of the flexible casing, are particularly beneficial when designing a flexible energy storage device for integration into a forming-fitting substrate such as a garment, wearable device or other flexible article of manufacture. In accordance with a first aspect the invention provides a flexible electrochemical energy storage device comprising at least two separated electrodes and an electrolyte contained within a flexible casing having an inside surface facing the electrolyte, wherein the flexible casing comprises a multi-layer laminate comprising: a polymeric seal layer at the inside surface of the flexible casing, wherein the polymeric seal layer is chemically inert to the electrolyte; a barrier layer comprising a semi-crystalline polymeric film and a water-impervious metallic or inorganic film; and a dampening layer comprising a substantially amorphous polymer with a Tg below 35°C, wherein the dampening layer dampens sound produced when flexing the flexible casing. In some embodiments, the dampening layer has a thickness of between 10 pm and 200 pm, such as between 30 pm and 100 pm. In some embodiments, the substantially amorphous polymer has a Tg below 30°C, such as below 25°C. In some embodiments, the substantially amorphous polymer is selected from the group consisting of an acrylate polymer, an epoxy polymer, a mixed acrylateepoxy polymer, a silicone polymer, a plastisol and a thermoplastic polymer. The acrylate polymer may be a polymer of (i) at least one selected from the group consisting of a urethane di- or poly(meth)acrylate, a polyalkylene oxide-linked di-or poly(meth)acrylate, a (meth)acrylated epoxidized triglyceride, and (ii) optionally a reactive diluent. The epoxy polymer may be a polymer of at least one selected from the group consisting of a bisphenol epoxy resin and an aliphatic epoxy resin. The mixed acrylate-epoxy polymer may be a polymer of (i) one or more selected from the group consisting of a urethane di- or poly(meth)acrylate, a polyalkylene oxide-linked di- or poly(meth)acrylate, a (meth)acrylated epoxidized triglyceride, (ii) one or more selected from the group consisting of a bisphenol epoxy resin and an aliphatic epoxy resin, and (iii) optionally a reactive diluent. The thermoplastic polymer may be selected from the group consisting of a polyurethane, poly(styrene-butadiene-styrene) (SBS) and poly(styrene-ethylene-butylene-styrene) (SEBS). In some embodiments, the dampening layer is positioned between the barrier layer and an outside surface of the flexible casing. In some embodiments, the dampening layer is at the outside surface of the flexible casing. In some embodiments, the polymeric seal layer is present on the entire inside surface of the flexible casing. In some embodiments, the flexible casing is hermetically sealed along at least a portion of its periphery by a seal formed by the polymeric seal layer, preferably wherein the seal hermetically seals two portions of multi-layer laminate together. In some embodiments, the polymeric seal layer comprises a heat-activatable adhesive polymer, optionally selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, acid modified polyethylene or polypropylene, acid copolymers of polyethylene or polypropylene and ethylenevinyl acid copolymers. In some embodiments, the semi-crystalline polymeric film is a biaxially-oriented polymeric film. In some embodiments, the semi-crystalline polymeric film has a thickness of less than about 20 pm, such as between 5 pm and 15 pm. In some embodiments, the semi-crystalline polymeric film comprises a polymer selected from the group consisting of a polyester, a polyolefin and a polyamide. The polyester may be selected from polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). The polyolefin may be selected from polypropylene and polyethylene. The polyamide may comprise at least one selected from polyamide 6 (polycaprolactam), polyamide 66 (polyhexamethylene adipamide), polyamide 610 and polyamide-MXDX (polyxylylene adipamide). In some embodiments, the semi-crystalline polymeric film is a biaxially oriented polypropylene (BOPP) film or a biaxially oriented polyethylene terephthalate (BOPET) film. In some embodiments, the water-impervious metallic or inorganic film is a coating on the semi-crystalline polymeric film. The coating may be produced on the semicrystalline polymeric film by vapor deposition, for example by a vapor deposition technique selected from vacuum deposition, electron beam deposition and plasma enhanced chemical vapour deposition. The coating may have a thickness of less than about 100nm, such as between 20nm and 70nm. In some embodiments, the water-impervious metallic or inorganic film is selected from the group consisting of (i) a metallic film comprising aluminium, (ii) an oxide film selected from aluminium oxide, tin oxide, silicon oxide and mixtures thereof, and (iii) a nitride film selected from aluminium nitride, silicon nitride and mixtures thereof. In some embodiments, the multi-layer laminate comprises one or more further barrier layers, each further barrier layer comprising a semi-crystalline polymeric film and a water-impervious metallic or inorganic film. The barrier layer and at least one further barrier layer may be adhered together by an adhesive interlayer, preferably with their respective water-impervious metallic or inorganic films facing each other. In some embodiments, the dampening layer is adhered to the barrier layer, for example to the semi-crystalline polymeric film of the barrier layer. The semicrystalline polymeric film of the barrier layer may be surface-activated, for example by a method selected from corona discharge treatment, plasma treatment, flame treatment and dielectric barrier discharge treatment, to enhance adhesion of the dampening layer to the barrier layer. The barrier layer may be primed with a primer composition, for example in an amount of less than 2g / m2, to enhance adhesion of the dampening layer to the barrier layer. In some embodiments, the multi-layer laminate has a water vapour transmission rate of less than 200 mg / m2 / day, such as less than 100 mg / m2 / day, as measured by ASTM F3299-18. In some embodiments, a specimen comprising two laminated sheets of the multilayer laminate has a flexural rigidity of less than 3000 pN.m, or less than 2000 pN.mm, or less than 2000 pN.m, as measured by AS 2001.2.9. In some embodiments, the flexible casing is in the form of a planar pouch formed from one or more sheets of the multi-layer laminate. In some embodiments, each electrode comprises a flexible current collector, preferably a fabric current collector. The flexible current collector may be an electrically conductive woven fabric current collector, such as a woven carbon cloth comprising graphotic carbon fibre. The flexible current collector may comprise a terminal portion of the woven fabric which passes through the flexible casing to provide an electrical terminal for the flexible lithium-ion battery. The flexible casing may be sealed against ingress of air or egress of the electrolyte where the terminal portion passes through the flexible casing by a polymeric sealant infiltrated through the weave of the woven fabric. The polymeric sealant may be a heat-activated thermoplastic, such as a polyolefin, for example a polyethylene such as linear low density polyethylene. Each electrode may comprise an electroactive composition supported on the flexible current collector, the electroactive composition comprising an anode or cathode material, a polymeric binder and optionally a conductive additive. In some embodiments, the flexible electrochemical energy storage device is a lithium-ion secondary battery. In accordance with a second aspect the invention provides a method of producing a flexible electrochemical energy storage device, the method comprising: (i) providing a multi-layer laminate comprising: a polymeric seal layer at one surface of the multi-layer laminate; a barrier layer comprising a semi-crystalline polymeric film and a water-impervious metallic or inorganic film; and a dampening layer comprising a substantially amorphous polymer with a Tg below 35°C; (ii) producing a flexible casing from the multi-layer laminate, wherein the polymeric seal layer is located at an inside surface of the flexible casing; (iii) functionally arranging at least two separated electrodes and an electrolyte within the flexible casing; and (iv) hermetically sealing the flexible casing. In some embodiments, (i) providing the multi-layer laminate comprises coating the barrier layer with a coating composition and curing and / or drying the coating composition to form the dampening layer adhered to the barrier layer. The barrier layer may be coated with the coating composition in a roll-to-roll coating process. In some embodiments, the method further comprises priming the barrier layer with a primer composition, before coating the barrier layer with the coating composition, to enhance adhesion of the dampening layer to the barrier layer. In some embodiments, (i) providing the multi-layer laminate comprises laminating the barrier layer to one or more further barrier layers, each further barrier layer comprising a semi-crystal line polymeric film and a water-impervious metallic or inorganic film, by one or more adhesive interlayers. The barrier layer and one further barrier layer may be adhered together with their respective water-impervious metallic or inorganic films facing each other. In some embodiments, (i) providing the multi-layer laminate comprises laminating the polymeric seal layer to the barrier layer with one or more adhesive interlayers. In accordance with a third aspect the invention provides a flexible article of manufacture comprising a flexible electrochemical energy storage device according to any embodiment of the first aspect. In some embodiments, the flexible electrochemical energy storage device is integrated into a flexible fabric portion of the flexible article of manufacture. In some embodiments, the flexible article of manufacture is a garment. Where the terms “comprise”, “comprises” and “comprising” are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof. Further aspects of the invention appear below in the detailed description of the invention. Brief Description of Drawings Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which: Figure 1 schematically depicts, in side cross-sectional view, a flexible electrochemical energy storage device according to some embodiments of the invention. Figure 2 schematically depicts, in plan view, the flexible electrochemical energy storage device of Figure 1. Figure 3 schematically depicts, in side cross-sectional view, a precursor multilayer laminate as prepared in Example 1. Figure 4 schematically depicts, in side cross-sectional view, a multi-layer laminate for a flexible casing of a flexible electrochemical energy storage device according to some embodiments of the invention. Multi-layered laminates having the structure depicted in Figure 4 were prepared in Examples 2 and 3. Figure 5 schematically depicts, in side cross-sectional view, a precursor multilayer laminate as prepared in Example 4. Figure 6 schematically depicts, in side cross-sectional view, a multi-layer laminate for a flexible casing of a flexible electrochemical energy storage device according to some embodiments of the invention. A multi-layered laminate having the structure depicted in Figure 6 was prepared in Example 5. Figure 7 schematically depicts a sheet of carbon cloth with polyethylene tab seals, vertically mounted for spraying with electrode precursor slurry, as done in Example 6. Figure 8 is a low magnification SEM image showing the infiltration of molten polyethylene from a heat activated polyethylene tab seal through the weave of a woven carbon cloth comprising graphitic carbon fibre, as produced in Example 7. Figure 9 is a high magnification SEM image showing the infiltration of molten polyethylene from a heat activated polyethylene tab seal into into the internal porosity of a multifilamentous yarn in a woven carbon cloth comprising graphitic carbon fibre, as produced in Example 7. Detailed Description The invention relates to a flexible electrochemical energy storage device which comprises at least two separated electrodes and an electrolyte contained within a flexible casing. The flexible casing has an inside surface which faces, and is typically in contact with, the electrolyte and an outside surface which will be exposed to the environment surrounding the device. The flexible casing comprises a multi-layer laminate comprising the following layers: (i) a polymeric seal layer positioned at the inside surface of the flexible casing, the polymeric seal layer being chemically inert to the electrolyte; (ii) one or more barrier layers, each barrier layer comprising a semi-crystalline polymeric film and a water-impervious metallic or inorganic film; and (iii) a dampening layer comprising a substantially amorphous polymer with a glass transition temperature (Tg) below 35°C. The dampening layer dampens the sounds produced when the flexible casing is flexed, thus reducing the crinkling or rustling types of noises produced when the flexible electrochemical energy storage device is subjected to movement. The dampening layer may also impart improved drape characteristics to the multi-layer laminate, so that the flexible electrochemical energy storage device is more suited to integration into flexible, fabric-based articles of manufacture such as garments. A flexible electrochemical energy storage device according to some embodiments disclosed herein is schematically depicted in Figures 1 and 2. Flexible electrochemical energy storage device 100 comprises flexible electrode 110 and flexible electrode 112, separated by a porous flexible separator 114. The sheetlike electrodes and separator are functionally arranged inside flexible casing 118, which is in the form of a planar pouch fabricated from sheet portions 132 and 134 of a multi-layered laminate. The multi-layered laminate has a particular construction which will be described below. The flexible casing contains electrolyte 120, such as a liquid electrolyte, to provide ionic conductivity between the electrodes. The electrolyte is thus in contact with the electrodes, the separator and typically also the inside surface of the flexible casing. The device components appear spaced apart in Figure 1, for greater clarity, but it will be appreciated that the sheet-like electrodes, separator and laminate walls of the flexible casing are overlaid in close contact so that flexible electrochemical energy storage device 100 has a generally flat, yet flexible, configuration. Electrode 110 comprises a flexible current collector 122 with an electroactive composition 124 supported thereon. Similarly, electrode 112 comprises a flexible current collector 126 with an electroactive composition 128 supported thereon. Both current collectors may optionally be conductive fabrics. Electrodes 110 and 112 comprise current collector tabs 130 which are extensions of the flexible current collectors 122, 126 that are not coated with electroactive composition. In some exemplary embodiments, device 100 is a lithium-ion battery, in which case electroactive composition 124 comprises a particulate cathode material (e.g. LiFePO4; LFP), electroactive composition 128 comprises a particulate anode material (e.g. Li4TisOi2; LTO) and electrolyte 120 comprises mobile lithium ions. Electroactive compositions 124, 128 may also include a polymeric binder and conductive additive. As best seen in Figure 2, flexible casing 118 is a planar pouch of generally rectangular configuration, formed by two sheet portions 132, 134 (optionally folded halves of a single sheet) of multi-layer laminate which are heat-sealed together in heat sealed regions 136 around the periphery of flexible casing 118. The current collector tabs 130 extend through one sealed edge of the planar pouch to provide electrical terminals of the device. Sheet portions 132, 134 are carefully sealed onto current collector tabs 130 in tab seal regions 138 to avoid or limit air and moisture ingress or electrolyte leakage at the location where the current collector tabs pass through flexible casing 118. Multi-layer laminate The flexible casing comprises, and is typically formed from, a multi-layer laminate. As used herein, a multi-layer laminate refers to a sheet comprising multiple layers of film which are adhered together. Figure 4 schematically depicts a multi-layer laminate 300 used in the flexible electrochemical energy storage device according to some embodiments of the invention. Multi-layer laminate 300 comprises two barrier layers 308, each barrier layer comprising a semi-crystalline polymeric film 310, for example a biaxially-oriented polyethylene terephthalate (BOPET) film and a water-impervious metallic or inorganic film 312, for example metallic aluminium. Metallic or inorganic film 312 may be formed as a coating on polymeric film 310 with a thickness of less than about 100 nm. The two barrier layers 308 are adhered together by a thin (1-2 pm) adhesive interlayer 314, for example a two part polyurethane adhesive, with their respective water-impervious metallic or inorganic films 312 facing each other. Multi-layer laminate 300 further comprises a polymeric seal layer 316, which is adhered to the semi-crystalline polymeric film 310 of one of the barrier layers 308 by another adhesive interlayer 314. The flexible casing is constructed with the multi-layer laminate oriented to position the polymeric seal layer at the inside surface of the flexible casing, so that the polymeric seal layer faces and is typically exposed to the electrolyte. Polymeric seal layer 316 thus comprises, and is typically formed of, a polymeric material which is chemically inert to the electrolyte to be used in the flexible energy storage device. Because the polymeric seal layer extends as a continuous layer across the laminate, it will be present on the entire inside surface of the flexible casing and can thus seal liquid electrolytes within the flexible energy storage device. Polymeric seal layer 316 may comprise a heat-activatable adhesive polymer, for example linear low density polyethylene (LLDPE) or other suitable heat-activatable polymers known in the art, which can be used to heat-seal portions of the laminate together to form the flexible case, as will be described in greater detail hereafter. Multi-layer laminate 300 further comprises a dampening layer 318 which comprises, and is typically formed of, a substantially amorphous polymer. The flexible casing is constructed with the multi-layer laminate oriented to position dampening layer 318 at the outside surface of the flexible casing. The substantially amorphous polymer, for example a polyurethane acrylate, exhibits a glass transition close to or below room temperature, so that the polymer will be at least partially in its rubbery state at typical operating conditions of the flexible energy storage device. The substantially amorphous polymer thus has a glass transition temperature (Tg) of below 35°C. As a result of the two barrier layers and the polymeric seal layer, multi-layer laminate 300 is suitably resistant to permeation of gases and leakage of liquids through the flexible casing. The two barrier layers are arranged with their water-impervious metallic or inorganic films facing each other and thus separated only by a very thin adhesive interlayer. This arrangement is expected to improve the permeability characteristics of the multi-layer laminate in comparison to a laminate having a single barrier layer only, since any defects in the water-impervious metallic or inorganic films 312, 314 of the barrier layers are unlikely to align sufficiently to provide a facile permeation pathway through the laminate structure. In addition, the semi-crystalline polymeric films of each barrier layer contribute to the laminate’s permeation-resistance because of the in-plane molecular chain ordering produced by the biaxial orientation of the film. Multi-layer laminate 300 may thus have a water vapour transmission rate of less than 100 mg / m2 / day, as measured by ASTM F3299-18. Figure 6 schematically depicts a multi-layer laminate 500 used in the flexible electrochemical energy storage device according to other embodiments of the invention, comprising barrier layer 508, polymeric seal layer 516, and dampening layer 518. Differently from laminate 300, multi-layer laminate 500 includes only one barrier layer 508, which is composed of a semi-crystalline polymeric film 510, for example a biaxially-oriented polyethylene terephthalate (BOPET) film, and a water-impervious metallic or inorganic film 312, for example a thin coating of aluminium oxides on the BOPET film. Polymeric seal layer 516 is adhered to the semi-crystalline polymeric film 510 of the barrier layer by adhesive interlayer 514. Dampening layer 518 is thus adhered to the barrier layer on the side of water-impervious metallic or inorganic film 512. In multi-layer laminates having the structure of either multi-layer laminate 300 or 500, the addition of the dampening layer (318, 518) improves the flexibility of the laminate structure, providing the laminate with “hand-feel” and drape characteristics which more closely resemble a fabric than an equivalent laminate without this added layer. It has been observed that relative differences in the apparent flexibility of laminates correspond to differences in the bending modulus, for example as measured according to AS 2001.2.9, and this parameter can be used to validate the advantages provided by the dampening layer. Furthermore, the dampening layer effectively dampens the noises produced when the multilayer laminate is flexed or otherwise subjected to movement. Without wishing to be bound by any theory, the inventors attribute the crackling sounds produced in the absence of the dampening layer to movements of the crystalline regions in the semi-crystalline polymeric film in the barrier layer, and propose that the substantially amorphous, low Tg polymer of the dampening layer acts as a massdampening composition which dampens sound-producing motions of the semicrystalline polymeric film and absorbs noises which are emitted. Barrier layer The multi-layer laminate used in the flexible casing comprises at least one barrier layer comprising a semi-crystalline polymeric film and a water-impervious metallic or inorganic film. As used herein, a semi-crystalline polymeric film refers to a film composed of a solid polymer in which the molecular chains are partially ordered in crystalline regions, including via crystallisation from the melt or by alignment under tensile stresses in the solid state (e.g. during extrusion of the film). Typically, the degree of crystallinity in a semi-crystalline polymer is between 10% and 80%. As used herein, a water-impervious metallic or inorganic film refers to a thin but substantially continuous film of a metallic composition or one or more inorganic compounds which inhibits the permeation of water vapour through the film. The water-impervious metallic or inorganic film is typically a thin but continuous coating formed on a surface of the semi-crystalline polymeric film. The coating generally has a thickness of less than about 150 nm, or less than 10Onm, such as between 20nm and 70nm, and must therefore be supported by a semi-crystalline polymeric film which provides the necessary mechanical properties of the barrier layer. This arrangement can be distinguished from foil laminates where one or more relatively thick (e.g. >10 pm), self-supporting metallic foils is laminated to polymeric layers to form a foil laminate structure. While such foil laminates can have excellent barrier properties, they are insufficiently flexible for integration into fabric-based articles of manufacture such as garments. In some embodiments, the water-impervious metallic or inorganic film is a metallic film. The metallic film may comprise, or consist of, metallic aluminium. In other embodiments, the water-impervious metallic or inorganic film is an inorganic film. The inorganic film may comprise a metal oxide, such as aluminium oxide, tin oxide, silicon oxide and mixtures thereof, or a metal nitride, such as aluminium nitride, silicon nitride and mixtures thereof. Suitably continuous and thus water-impervious metallic, metal oxide and metal nitride coatings may be produced on the semi-crystalline polymeric film by techniques known in the art. In some embodiments, the coatings are produced by vapor deposition, for example by a vapor deposition technique selected from vacuum deposition, electron beam deposition and plasma enhanced chemical vapour deposition. In some embodiments, the semi-crystalline polymeric film has a thickness of less than about 20 pm, such as between 5 pm and 15 pm. In this range of thicknesses, semi-crystalline polymeric film may provide a good balance between flexibility and robustness. In some embodiments, the semi-crystalline polymeric film is a biaxially-oriented polymeric film. Biaxially-oriented polymeric films are produced via an extrusion process in which the extruded film is stretched in both the machine and transverse directions. The effect of this is to orient and align the molecular chains of the polymer in the plane of the film, thus improving the barrier properties of the film against water vapour and / or oxygen permeation. In some embodiments, the semi-crystalline polymeric film comprises a polymer selected from the group consisting of a polyester, a polyolefin and a polyamide. The polyester may be polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), preferably PET. The polyolefin may be polypropylene or polyethylene, preferably polypropylene. The polyamide may be polyamide 6 (polycaprolactam), polyamide 66 (polyhexamethylene adipamide), polyamide610 or polyamide-MXDX (polyxylylene adipamide). Particularly preferred semicrystalline polymeric films include biaxially oriented polypropylene (BOPP) film and biaxially oriented polyethylene terephthalate (BOPET) film. The multi-layer laminate may comprise one barrier layer or multiple barrier layers, for example two. Where multiple barrier layers are used, each barrier layer may comprise a semi-crystalline polymeric film and a water-impervious metallic or inorganic film, as described herein. Typically, the barrier layers will be adjacent in the laminate, for example adhered directly together by only a very thin adhesive interlayer. In some embodiments, two barrier layers in the multi-layer laminate are laminated together face-to-face, such that their water-impervious metallic or inorganic films are adjacent. As already noted, this arrangement has the advantage of reducing gas permeability even if there are defects, such as pinholes, present in each of the metallic or inorganic films. Primarily as a result of the one or more barrier layers in the laminate structure, the multi-layer laminate is able to resist the permeation of one or more gases into the interior of the flexible casing, such as water vapour and / or oxygen. The multilayer laminate may have a water vapour transmission rate (WVTR) of less than 200 mg / m2 / day, such as less than 100 mg / m2 / day, as measured by ASTM F3299-18. Flexible lithium-ion batteries packaged in flexible casings constructed from multi-layer laminates with WVTR values in this range have been found capable of sustained electrochemical cycling performance. Polymeric seal layer The multi-layer laminate used in the flexible casing comprises a polymeric seal layer, present at the inside surface of the flexible casing. The polymeric seal layer may have a thickness of less than about 100 pm, such as between 40 pm and 80 pm. The role of this layer is to cover and seal the inside surface of the flexible casing, thus preventing electrolyte leakage or electrolyte-induced degradation of other layers of the laminate. Furthermore, the polymeric seal layer may facilitate the fabrication of the flexible casing from the multi-layer laminate by adhering two multi-layer laminate portions together e.g. by heat-sealing. To meet these requirements, the polymeric composition of the polymeric seal layer should be chemically inert and substantially impermeable to the electrolyte, particularly when the electrolyte is a liquid or gel to which the polymeric seal layer is directly exposed. Furthermore, to facilitate the fabrication of the flexible casing, the polymeric seal layer may comprise a heat- or pressure-activatable adhesive polymer, preferably a heat-activatable adhesive polymer, i.e. a thermoplastic polymer which softens sufficiently when heated to allow intermixing with another similar layer and which hardens again when cooled to form a heat-seal bond. Non-limiting examples of suitable types of chemically inert and adhesive polymers include polyethylene, polypropylene, ethylene-propylene copolymer, acid modified polyethylene or polypropylene, acid copolymers of polyethylene or polypropylene and ethylene-vinyl acid copolymers. Dampening layer The multi-layer laminate used in the flexible casing includes a dampening layer comprising a substantially amorphous polymer. As used herein, a substantially amorphous polymer is a solid polymer in which the molecular chains are substantially disordered (and thus not ordered in the crystalline regions characteristic of a semi-crystalline polymer). The degree of crystallisation in an amorphous polymer is generally so low that the polymer does not exhibit any observable crystalline structures in X-ray or electron scattering analyses. The substantially amorphous polymer exhibits a glass transition close to or below room temperature, so that the polymer will generally be at least partially in its rubbery state at typical operating conditions of the flexible energy storage device. The substantially amorphous polymer thus has a glass transition temperature (Tg) of below 35°C. Tg values may be determined according to ASTM E1356-08 “Standard Test Method for Assignment of the Glass Transition temperatures by Differential Scanning Calorimetry”. In some embodiments, the Tg is below 30°C, or below 25°C, such as below 20°C. In some embodiments, the Tg is above 0°C, such as above 10°C, so that the substantially amorphous polymer is not too tacky. In some embodiments, the dampening layer has a thickness of between 10 pm and 200 pm, such as between 30 pm and 100 pm. In such ranges, the dampening layer has sufficient mass per unit area to effectively dampen and modulate the flexibility of the barrier layer(s) in the multi-layer laminate, yet is not so bulky as to unacceptably increase the overall thickness of the multi-layer laminate. The substantially amorphous polymer may be a thermoset or a thermoplastic polymer. In some embodiments, it is a thermoset polymer. A wide range of chemical compositions may be suitable, including acrylate polymers, epoxy polymers, mixed acrylate-epoxy polymers, silicone polymers, plastisols and thermoplastic polymers. In some embodiments, the substantially amorphous polymer is an acrylate polymer. The acrylate polymer may be a polymer of a urethane di- or poly(meth)acrylate, a polyalkylene oxide-linked di- or poly(meth)acrylate, or a (meth)acrylated epoxidized triglyceride prepolymer, optionally copolymerised together with a reactive diluent. In some embodiments, the acrylate polymer is a polyurethane acrylate. The acrylate polymer may be polymerised (cured) under radiation, such as UV-light, in the presence of suitable photoinitiators. In some embodiments, the substantially amorphous polymer is an epoxy polymer. The epoxy polymer may be a polymer of a bisphenol epoxy resin or an aliphatic epoxy resin, typically cured with polyamine hardeners. In some embodiments, the substantially amorphous polymer is a mixed acrylateepoxy polymer. The mixed acrylate-epoxy polymer may be a polymer of a urethane di- or poly(meth)acrylate, a polyalkylene oxide-linked di- or poly(meth)acrylate, (meth)acrylated epoxidized triglyceride in combination with a bisphenol epoxy resin or an aliphatic epoxy resin, optionally copolymerised together with a reactive diluent. The mixed acrylate-epoxy polymer may be polymerised (cured) under radiation, such as UV-light, in the presence of suitable photoinitiators. In some embodiments, the substantially amorphous polymer is a thermoplastic polymer. Examples of suitable thermoplastic polymers include thermoplastic polyurethane, thermoplastic poly(styrene-butadiene-styrene) (SBS) and thermoplastic poly(styrene-ethylene-butylene-styrene) (SEBS). In some embodiments, the dampening layer is produced as a coating on the multilayer laminate. Thus, a coating composition is applied to the adjacent layer of the multi-layer laminate and cured and / or dried thereon to provide the layer of substantially amorphous polymer. In some embodiments, the dampening layer is located on the opposite side of the barrier layer(s) from the polymeric seal layer. Thus, in the flexible casing, the dampening layer will be positioned between the barrier layer and the outside surface of the flexible casing, and is typically at the outside surface of the flexible casing. Adhesion The multi-layer laminate used in the flexible casing may comprise one or more adhesive and / or primer layers to enhance adhesion between the various layers present in the laminate. In some embodiments, the barrier layer(s) and the polymer seal layer are adhered together by a thin adhesive interlayer in a film lamination process (typically 1-2 pm thickness). Suitable adhesives for film lamination are known in the art, and include two-part polyurethane adhesives. In embodiments where the dampening layer is produced as a coating, the adjacent layer of the multi-layer laminate, typically a surface of the barrier layer, may be primed or surface-activated to enhance adhesion of the coating, thus reducing the risk of delamination. The barrier layer, and in particular a surface of its semicrystalline polymer film, may be primed with a primer composition, for example in an amount of less than 2g / m2, to enhance adhesion of the dampening layer to the barrier layer. Suitable primer compositions include commercially available polyurethane-based primers. Alternatively, or in addition, the semicrystalline polymeric film of the barrier layer may be surface-activated, for example by corona discharge treatment, plasma treatment, flame treatment or dielectric barrier discharge treatment, to enhance adhesion of the dampening layer to the barrier layer. Flexible casing The flexible casing of the flexible electrochemical energy storage device comprises, and is typically formed from, the multi-layer laminate. The flexible casing may be in the form of a substantially flat (i.e. planar) pouch produced from one or more sheets of the multi-layer laminate. Two sheets of the multi-layer laminate, or one sheet folded in half, may be heat sealed together around the periphery to form the pouch. Typically, the polymeric seal layer is a continuous layer across one surface of the multi-layered laminate, and will thus be present on the entire inside surface of the flexible casing. The seal layer is thus configured to seal liquid electrolytes within the flexible energy storage device, to avoid or limit electrolyte-induced degradation of other layers in the laminate, to avoid or limit contamination of the electrolyte by other layers in the laminate and to electrically insulate the flexible energy storage device. The dampening layer may be positioned between the barrier layer(s) and the outside surface of the flexible casing. In some embodiments, the dampening layer is at the outside surface of the flexible casing. Flexible electrochemical energy storage device The flexible electrochemical energy storage device, as disclosed herein, may be a battery or a supercapacitor, including hybrid and symmetrical supercapacitors. Such devices have in common that they include at least two separated electrodes and an electrolyte to provide ionic conductivity between the electrodes. The electrodes may be separated by an electrically insulating but porous separator which is infiltrated by the electrolyte, although it will be appreciated that a separator may not be required in all embodiments, for example where a solid polymeric electrolyte is used. The electrodes and the separator may each be flexible to ensure that the energy storage device as a whole is suitably flexible. In some embodiments, the electrodes and the separator are in the form of flexible sheets, with the flexible separator sheet interposed between the two electrode sheets. The electrodes may comprise a flexible current collector with an electroactive composition supported on the flexible current collector. In some embodiments, one or both flexible current collectors comprise a flexible electrically-conductive fabric. The fabric may be porous, as a result of voids between the fibres of the fabric, so that the electroactive composition can penetrate and thus integrate with the fabric current collector, and to facilitate penetration and wetting of the electrode by the electrolyte. The term fibre in this context encompasses multifilamentous fibres, threads and yarns. Flexible electrically-conductive fabrics produced by a range of known techniques are suitable, provided that the fabric adequately retains its electrical conductivity when subjected to flexing in normal use. In one set of embodiments, the flexible electrically-conductive fabric comprises electrically conductive fibres, for example metal-coated or carbon-based fibres, which are assembled into woven, nonwoven or knitted fabrics by known fabric-forming techniques. The flexible electrically-conductive fabrics may be formed entirely of such conductive fibres, or an array of conductive fibres or wires may be integrated into a woven or non-woven fabric comprising conventional non-conductive fibres. Fabric-based current collectors of this type are disclosed in US patent 8,192,863. In some embodiments, the flexible electrically-conductive fabric is a carbon-based fabric, for example a woven or non-woven fabric of graphitic carbon fibre or carbon nanotubes. In some embodiments, the flexible electrically-conductive fabric is a woven fabric, for example a woven cloth comprising a weave of electrically conductive fibres. An example of a suitable fabric according to both these embodiments is a woven carbon cloth with a high graphitic carbon content, such as HCB 1170 from AvCarb (plain weave, electric resistivity 1.1x10 3 ohm-cm, 99.5% carbon content). Such a fabric has been found to provide a good balance of properties, including flexibility, low resistivity and good susceptibility to penetration by an electrode precursor slurry so that a uniform layer of electroactive composition can be supported on the carbon cloth with the electroactive composition intimately interspersed through the weave of graphitic carbon fibre in the carbon cloth. In other embodiments, one or both flexible current collectors are metallised fabrics, for example a non-conductive fabric which has been sputter-coated with a metal such as gold or copper to deposit a semi-continuous metallic layer with sufficient connectivity to provide conductive pathways across the fabric substrate. It is also envisaged that the flexible current collector may be a continuous metallic film, for example a foil or metallised layer on a flexible polymeric film, although such two-dimensionally continuous coatings may be less desirable due to the lack of porosity and resultant risk of delamination of the electroactive composition. The flexible current collector may comprise a current collector tab, which is typically not coated with the electroactive composition, configured as a terminal for electrical connection of the electrochemical storage device to an external circuit. In the case of a fabric-based current collector, the tab may be a strip of the fabric which extends from the main portion of the fabric current collector which bears a layer of electroactive composition. The flexible current collectors of the electrodes may be dimensioned, with respect to the flexible casing, such that the current collector tab extends through the walls of the flexible casing, for example through the sealed edge of a planar pouch formed by two layers of multi-layer laminates. The laminate walls of the flexible casing should therefore be carefully sealed onto the tab seals to avoid or limit air and moisture ingress or electrolyte leakage at the location where the electrical connections pass through the flexible casing. As will be described in greater detail hereafter, the use of fabric current collectors provides the opportunity to effectively heat-seal the multi-layer laminate to the current collector tab by infiltrating the porosity of the fabric with a heat-activated polymer seal. The electroactive composition supported on the flexible current collector may comprise conventional electrode materials for supercapacitors or batteries. Typically, the electrode material is in particulate form, and the electroactive composition further comprises a polymeric binder to consolidate the electrode material and to adhere a layer of the electroactive composition to the flexible current collector. Examples of suitable polymeric binder are polyvinylidene difluoride (PVDF) or polyurethane. A low tensile modulus polyurethane, such as Pellethane 2102-85A, available from Dow, has been found particularly suitable as the flexibility of the resultant electrode is not restricted by the binder rigidity. The electroactive composition may also comprise a conductive additive, typically also in particulate form, to improve the electrical conductivity of the electroactive composition and its electrical contact with the flexible current collector. The conductive additive may be a carbon-based particulate, such a carbon black. In some embodiments, the electrode material in the electroactive composition of each electrode is a capacitive electrode material, as appropriate for supercapacitor electrodes. The capacitive electrode material may include either or both of a carbon-based electrode material and a pseudocapacitive electrode material. Carbon-based electrode materials having both high surface areas (such as between about 100 and 2500 m2 / g) and high conductivity, are particularly suitable for electric double-layer capacitors (EDLC devices), in which energy storage primarily occurs by separation of charge in a Helmholtz double layer at the interface between the surface of the conductive electrode material and the electrolyte. Carbon-based capacitive electrode materials may include reduced graphene oxide, graphene, exfoliated graphite, porous carbon and / or activated carbon. Pseudocapacitive materials, by comparison, store energy via rapidly reversible redox or intercalation processes involving electrolyte ions that occur at the surface of the electrode material. In some embodiments, the flexible energy storage device is a battery, such as a lithium-ion battery, and the at least two electrodes thus include an anode and a cathode. The electroactive composition of the anode and cathode will therefore include an anode electrode material and a cathode electrode material, respectively. Any of the known types of anode materials suitable for use in batteries may be used as the electrode material for the anode. In some embodiments, the anode material comprises an electroactive substance which is capable of reversibly intercalating / deintercalating lithium ions, such graphite, graphite composites with silicon, lithium metal, alloys of lithium metal, lithiated carbonaceous materials (such as lithiated graphites, activated carbons, hard carbons and the like), lithium intercalating metal oxide based materials such as lithium titanate (Li4TisOi2; LTO), metal alloys such as Sn-based systems and conducting polymers, such as n-doped polymers, including polythiophene and derivatives thereof. Any of the known types of cathode materials suitable for use in batteries may be used as the electrode material for the cathode. In some embodiments, the cathode material comprises an electroactive substance which is, for example, a compound capable of reversible lithium intercalation and deintercalation. Of particular interest are lithium intercalating metal oxide materials. Preferred examples of cathode materials include olivine type materials of general formula LiMPO4, where M is Fe, Co, Mn, and Ti. Specific examples include LiCoO2, LiMn2O4, LiFePO4 (LFP), and LiNiO2. Other examples include LiNiCoAIO2 (NCA), LiNiCoMnO2 (NMC), lithium manganese iron phosphate (LMFP), LiMn2O4 (LMO), LiNio.5Mm.5O4 (LMNO), LiMn2O4, LiMnNiO4 and analogues thereof or conducting polymers, redox conducting polymers, capacitor cathode materials, and combinations thereof. Examples of lithium intercalating conducting polymers are polypyrrole, polyaniline, polyacetylene, polythiophene, and derivatives thereof. Examples of redox conducting polymers are diaminoanthroquinone, poly metal Schiff-base polymers and derivatives thereof. The electroactive composition may be supported on the flexible current collector by applying an electrode precursor slurry to the flexible current collector, for example by coating, doctor blading, spraying, printing or other suitable techniques. The electrode precursor slurry typically comprises the electrode material (including precursors which can form an active electrode material in situ), a polymeric binder and optionally a conductive additive dispersed in a solvent. The flexible electrochemical energy storage device may comprise a separator to separate the electrodes. Where the electrodes are configured as flexible sheets, the separator may be an electrically insulating but porous flexible sheet interposed between the electrodes. Suitable separators, such as porous polymeric membranes and non-woven fabrics, are well-known in the battery art. The flexible electrochemical energy storage device comprises an electrolyte, which may generally be any electrolyte suitable for battery or supercapacitor applications provided that it is compatible with the types of electrodes present in the device. Both electrodes are in contact with the electrolyte, which thus provides ionic conductivity between the electrode materials of the electrodes. The electrolyte may be a liquid electrolyte, including liquid electrolytes comprising aprotic molecular solvents, such as carbonates, water or ionic liquids, such as the pyrrolidinium-based ionic liquids disclosed in WO2004 / 082059. In embodiments where the flexible electrochemical energy storage device is a lithium-ion battery, the electrolyte comprises mobile lithium ions, provided for example by dissolution of a lithium salt such as LiPFe in the electrolyte. In some embodiments, the electrolyte is a non-aqueous electrolyte comprising mobile lithium ions. The flexible electrochemical energy storage device may comprise one cell or multiple cells, so that more than two electrodes may be enclosed within the flexible casing. Method of producing a flexible electrochemical energy storage device The invention further relates to a method of producing a flexible electrochemical energy storage device. The method comprises providing a flexible multi-layer laminate comprising: a polymeric seal layer at one surface of the multi-layer laminate; a barrier layer comprising a semi-crystalline polymeric film and a water-metallic or inorganic film; and a dampening layer comprising a substantially amorphous polymer with a Tg below 35°C. The method further comprises steps of producing a flexible casing from the multi-layer laminate, wherein the polymeric seal layer is located at an inside surface of the flexible casing; functionally arranging at least two separated electrodes and an electrolyte within the flexible casing; and hermetically sealing the flexible casing. Providing the multi-layer laminate may comprise one or more steps of laminating pre-existing films together to form layers of the multi-layer laminate. Laminating steps may include (i) laminating together two or more barrier layers as described herein, preferably face-to-face with their water-impervious metallic or inorganic films facing each other, and (ii) laminating the barrier layer(s) to a polymeric seal layer, as described herein. The lamination step(s) may be conducted on conventional film laminating apparatus using known adhesives for film lamination, such as two-part polyurethane adhesives. Providing the multi-layer laminate may further comprise one or more steps of producing a coating on a pre-existing layer of the laminate. In particular, the dampening layer of the multi-layer laminate may be formed by coating another layer of the laminate, typically a barrier layer as described herein, with a coating composition and curing and / or drying the coating composition to form the substantially amorphous solid polymer of the dampening layer adhered to the preexisting layer. The coating step(s) may be conducted on conventional film coating apparatus, for example a roll-to-roll coater equipped with a doctor blading system. Optionally, the layer which receives the coating composition may be primed or activated to improve the adhesion of the coating. For example, the surface of the semicrystalline polymeric film of the barrier layer may be primed with a primer composition, for example in an amount of less than 2g / m2, to enhance adhesion of the dampening layer to the barrier layer. Suitable primer compositions include polyurethane-based primers. Alternatively, or in addition, the surface of the semicrystalline polymeric film may be surface-activated, for example by corona discharge treatment, plasma treatment, flame treatment or dielectric barrier discharge treatment, to enhance adhesion of the dampening layer to the barrier layer. The flexible casing of the flexible electrochemical energy storage device is typically formed from the multi-layer laminate, with the polymeric seal layer located at and forming the inside surface of the flexible casing. In one exemplary embodiment, the pouch is formed from a single sheet of the multi-layered laminate. The sheet is folded in half, with the polymeric seal layer on the inside, and hermetically sealed together opposite the fold, for example using a heat sealer to activate the polymeric seal layer along the edges of the pouch. The two sides initially remain unsealed to form pouch openings. The pouch is suitably dimensioned to receive the electrodes and the separator, which are typically also in the form of planar sheets, with the conductive tabs of the electrodes protruding through one pouch opening. One pouch opening can thus be hermetically sealed over the electrode tabs to enclose the electrodes, separator and electrolyte inside the pouch, as depicted in Figure 2. Flexible article of manufacture The invention further relates to a flexible article of manufacture which comprises the flexible electrochemical energy storage device as disclosed herein. The flexible article of manufacture may comprise, or be formed primarily of, one or more layers of flexible fabric or polymer sheeting which may be required to flex in use. The flexible electrochemical energy storage device, optionally in the form of a planar pouch, may thus be integrated into the article of manufacture by placing it against or between these layer(s). The flexible electrochemical energy storage device of the present disclosure is particularly suited to such applications because of the balance of properties provided by its multi-layer laminate flexible casing, including flexibility, barrier properties, fabric-like drape characteristics and comparative noiselessness when flexed. The flexible article of manufacture may be any manufactured object containing a flexible portion into which it may be advantageous to integrate a power source. Non-limiting examples of suitable flexible article of manufacture include garments, such as jackets, wearable devices, personal monitoring devices for medical, health or fitness applications, medical equipment, military equipment, portable electronic devices, tents, flexible wall panels and so forth. In the case of garments, the flexible energy storage device should not adversely affect the textile properties of the host garment, compared to the host garment in the absence of the flexible energy storage device. Properties of the host garment that should be retained are thermal properties, mechanical properties of the fabric of the host garment, moisture management, barrier and airflow properties. This may be achieved by appropriate placement of the flexible energy storage device, but alternatively or additionally by design features of the flexible energy storage device. EXAMPLES The present invention is described with reference to the following examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein. Example 1. Manufacture of a laminate comprising a composite barrier layer (with metallic coating) and a heat seal layer. Two layers of aluminised biaxially-oriented polyethylene terephthalate (BOPET) film with a web width of 1500 mm were laminated together using a two-part solvent-free polyurethane (PU) adhesive on commercial laminating equipment operated by Perfection Packaging (Dandenong South, Victoria, Australia). Each layer included a BOPET film of about 12 pm thickness coated with a metallic aluminium film of about 20-70 nm thickness. The layers were oriented with the aluminium films adjacent, so that the BOPET films were present on the outer surfaces of the composite barrier laminate. A heat-activatable linear low density polyethylene (LLDPE) thin film, of about 60 pm thickness, was then laminated onto one BOPET surface of the composite barrier layer laminate using the same two-part solvent-free polyurethane adhesive and lamination equipment. The resultant laminate is termed laminate-1 in the following examples. As depicted in Figure 3, laminate-1 comprises BOPET films 310, metallic aluminium films 314, PU adhesive interlayers 314 and LLDPE layer 316. Example 2. Addition of a polyurethane acrylate dampening layer to laminate-T The following compounds were used to produce a coating composition for forming a polyurethane acrylate (PUA) dampening layer on laminate-1: (1) a low viscosity, aliphatic urethane diacrylate oligomer (Ebecryl 8402), purchased from Allnex Australia, (2) polyethylene glycol diacrylate (PEGDA 575, Mn = 575), from Sigma Aldrich, used as a reactive diluent to reduce viscosity and impart flexibility, (3) a liquid a-hydroxyketone photo initiator (2-hydroxy-2-methylpropiophenone; Darocur 1173), purchased from Ciba, (4) a solid bis-acyl phosphine photo initiator (bis(2,4,6-trimethylbenzoyl)-phenylphoshineoxide; Irgacure 819), purchased from Ciba, and (5) a defoamer (mixture of polysiloxanes and hydrophobic solids in polyglycol; BYK 028), purchased from Res Chern Technologies. The solid Irgacure 819 was first dissolved in the liquid Darocur 1173 (D1173) at a 35 / 65 mixing ratio under a gentle heat (approximately 40°C) with constant stirring. These photo initiators were chosen in part to matching the output of the UV source with the UV absorption of the photo initiator molecules. Ebecryl 8402 (UA, 450 g 85.5 wt%) and PEGDA 575 (50 g, 9.5 wt%) were thoroughly mixed before BYK 028 (5 g, 1.0 wt%) was added. The pre-mixed photo-initiators (20 g, 4 wt%) were then added and the combination was thoroughly mixed before sealing the container. After about 2 to 3 hours of resting, the formulation was again mixed thoroughly and then left overnight in a cupboard to deaerate. This coating composition was applied to the BOPET-surface of laminate-1 (cut to widths of 260 mm or 300 mm for coating) by means of a roll-to roll-coater (a modified 2.0 m Barrell tape casting line) using a 20 cm wide doctor blading system. A box with a Fusion I300MB UV lamp system was placed above to provide curing of the urethane acrylate coating at a cure rate of 0.1 to 0.13 W / cm2 The feed rate of the system was set at approximate 0.2 m / min, giving an irradiation time of approximately 180 sec. Air was extracted from the top of the box to the fume hood above via a duct, in addition to the integrated blower in the I300MB. A metal plate with recirculating water was placed in contact with the underside of the table directly below the UV source as a cooling source. A release film (silicone 5 coated parchment paper) was applied to the coated film before rolling onto the rewind roll to prevent sticking of the polymerised PUA coating and contamination of the LLDPE surface. The cured polyurethane acrylate layer was about 45-55 pm in thickness. The resultant laminate comprising laminate-1 with a dampening layer of 10 amorphous PUA is termed laminate-2 in the following characterisation and examples. As depicted in Figure 4, laminate-2 comprises BOPET films 310, metallic aluminium films 312, PU adhesive interlayers 314, LLDPE layer 316 and amorphous polyurethane acrylate layer 318. Selected properties of laminate-2 are shown in Table 1. 15 Table 1. Property Values Water vapour transmission rate (WVTR) at 87 ± 9 (in house analytical lab) 100% relative humidity (ASTM F3299-18) 63 ± 18 (external analytical lab) Thickness (pm) 135 Mass per unit area (g / m2) 145 Waterproofness to IP67 (35 psi) (ASTM D3393) YES Peel Strength Test (N / mm2) (ASTM D903) > 3.6 N / mm2 (1mm seam) Ball burst (N); and extension (mm) (ASTM D3787)a 122.83 (SD7.56); 10.13 (SD 0.4) Glass transition temperature (Tg, °C) of the amorphous PUA, measured by differential scanning calorimetryb 16.1 a modified as follows: Samples were clamped in a 25 mm diameter burst strength accessory on an Instron instrument. A 6.35 mm ball was pushed through the film using a head speed of 100mm / min (ASTM standard uses a 44.45mm diameter accessory with a 25mm ball) bASTM E1356-08 Example 3. Alternative polymers for the dampening layer. A range of alternative polymeric coatings were assessed for their potential suitability as dampening layers to dampen sound and / or increase the drapeability of flexible barrier laminates (such as laminate-1). Polymer systems evaluated included: 1. Epoxy based systems, including aromatic bisphenol A-based epoxy and aliphatic trimethylolpropane-based epoxy; 2. UV-curable polymer precursors, including resins based on acrylate and epoxy monomers. Acrylate monomers such as urethane acrylates and epoxy acrylates polymerise rapidly in the presence of photo-generated free radicals under oxygen diffusion-free conditions. Urethane acrylate polymers in particular are known for their flexibility, general environmental durability and adhesion; and 3. Thermoplastic polymers, applied by solvent casting, including polyurethanes, poly(styrene-butadiene-styrene) (SBS) and poly(styrene-ethylene-butylene-styrene) (SEBS). Selected examples of these systems were used to prepare dampening layers for laminates as follows. Epoxy based system (Laminate-3). Resin samples were prepared by thoroughly mixing Erisys GE-30 (trimethylolpropane triglycidyl ether) (73.22 wt.%), from Huntsman, N-aminoethyl piperazine (6.88 wt.%), from Sigma Aldrich, poly(propylene glycol) bis(2-aminopropyl ether) (18.26 wt.%), from Sigma Aldrich and tris(dimethyl aminomethyl)phenol (1.64 wt.%), from Polysciences, followed by degassing at room temperature using a rotary evaporator (between 15 to 20 minutes). The mixed resin was then applied to laminate-1 (BOPET surface) using a 20 cm wide doctor blading system and allowed to cure at room temperature. The cured epoxy layer was about 65 pm in thickness. The glass transition temperature (Tg, °C) of the amorphous epoxy layer, measured by differential scanning calorimetry, was 25.0°C. The resultant multi-layer laminate comprising laminate-1 with a dampening layer of amorphous epoxy polymer is termed laminate-3. Laminate-3 has a similar structure to laminate-2 depicted in Figure 4 except that amorphous polymeric layer 318 is an amine-cured epoxy polymer. UV-cured epoxy-acrylate system (Laminate-4). Resin samples were prepared by thoroughly mixing Erisys GE-30 (45.5 wt.%), acrylated epoxidized soybean oil (AESO) (45.5 wt.%) from SigmaAldrich with two photoinitiators D1173 (4.5 wt.%) and triarylsulfonium hexafluoroantimonate salts mixed 50% w / w in propylene carbonate (UVI-9676) (4.5% wt.%), from Sigma Aldrich. This mixture was degassed at room temperature using a rotary evaporator and the mixed resin was then applied to laminate-1 (BOPET surface) using a 20 cm wide doctor blading system and cured under a UV lamp (D bulb). The cured epoxy-acrylate layer was about 65 pm in thickness, and had a glass transition temperature (Tg) of 25.0°C. The resultant laminate comprising laminate-1 with a dampening layer of amorphous epoxy-acrylate polymer is termed laminate-4. Laminate-4 has a similar structure to laminate-2 depicted in Figure 4 except that amorphous polymeric layer 318 is a UV-cured epoxy-acrylate polymer. Thermoplastic polyurethane solvent casting (Laminate-5) Re-flex 585A polyether based thermoplastic polyurethane (TPU), available from Townsend Chemicals (Australia), was dissolved in tetrahydrofuran (THF) with the aid of a bottle roller with the final concentration being dependant on the viscosity (range 10-15% wt). This coating composition was applied to the BOPET-surface of laminate-1 by means of the roll-to roll-coater (a modified 2.0 m Barrell tape casting line) using a 20 cm wide doctor blading system at a feed rate of 0.9 m / min. The TPU layer was about 55 pm in thickness, and had a glass transition temperature (Tg) of between 10 and 20°C. The resultant laminate comprising laminate-1 with a dampening layer of amorphous TPU is termed laminate-5. Laminate-5 has a similar structure to laminate-2 depicted in Figure 4 except that amorphous polymeric layer 318 is a thermoplastic polyurethane polymer. Example 4. Manufacture of a laminate comprising a composite barrier layer (with inorganic vapour deposition film) and a heat seal layer. A laminate was produced using a transparent barrier film (GX-P-F, Toppan, Japan) comprising a single 12 pm thick biaxially-oriented polyethylene terephthalate (BOPET) film with an aluminium oxide film of about 20-70 nm thickness vapour deposited thereon as the barrier coating. The BOPET side of the barrier film was then laminated with Pll adhesive to a linear low density polyethylene (LLDPE) film of about 60 pm thickness by Toppan (Indonesia). The resultant laminate is termed laminate-6. As depicted in Figure 5, laminate-6 comprises BOPET film 510, aluminium oxide coating 512, PU adhesive interlayer 514 and LLDPE layer 516. Example 5. Addition of a polyurethane acrylate dampening layer to laminate-6. The coating composition of Example 2 was applied to laminate-6 (on the aluminium oxide coating side of the barrier film) and cured thereon as described in Example 2. The cured polyurethane acrylate layer was about 55 pm in thickness. The resultant laminate comprising laminate-6 with a dampening layer of amorphous PUA is termed laminate-7. Laminate-7 had a water vapour transmission rate (WVTR) of less than 15 mg / m2 / day, as measured by ASTM F3299-18. As depicted in Figure 6, laminate-7 comprises BOPET film 510, aluminium oxide coating 512, PU adhesive interlayer 514, LLDPE layer 516 and amorphous polyurethane acrylate layer 518. Example 4. Evaluation of mechanical and noise characteristics. Mechanical properties of laminates relevant to the flexibility and drape characteristics were assessed using a fixed angle flexometer apparatus typically used to determine the stiffness of cloth according to AS 2001.2.9 (Standards Australia: Methods of test for textiles Physical tests - Determination of stiffness of cloth). Test specimens were prepared by heat-laminating two of the laminates under investigation together face-to-face, to avoid errors introduced by curling of the samples. The bending length of test specimens (taken across the length and width of the laminates, where width refers to the width across the web) is measured and the flexural rigidity and bending modulus thus calculated. Four laminates were evaluated by this method: laminate-1 (double barrier layer with aluminium metal coatings; without PUA dampening layer), laminate-2 (double barrier layer with aluminium metal coatings; with PUA dampening layer), laminate-6 (single barrier layer with aluminium oxide coating; without PUA dampening layer), and laminate-7 (single barrier layer with aluminium oxide coating; with PUA dampening layer). For comparison, a sample of DEL35 (Dai Nippon Printing Company) was also evaluated; DEL35 is a foil-based barrier material for mobile phone pouch batteries, of total thickness less than 100 pm and which includes a 35 pm Al foil laminated between polymeric films. The mechanical properties are compared in Table 2. Table 2. Laminate test sample Flexural rigidity (pN.m) Bending modulus (pN.m2) Laminate-1 1886 (length) 2106 (width) 34371 (length) 38386 (width) Laminate-2 1936 (length) 2202 (width) 9034 (length) 10278 (width) Laminate-6 787 (length) 25302 (length) 925 (width) 29739 (width) Laminate-7 1047 (length) 1270 (width) 6919 (length) 8393 (width) DEL35 8622 (length) 9093 (width) 151820 (length) 160119 (width) DEL35 is substantially more rigid than laminates-1, -2, -6 and -7 due to the thick Al foil layer. Laminate 2 was qualitatively more drapeable than laminate-1, based on hand-feel, and this is reflected in the significant reduction in bending modulus 5 seen in Table 2. The flexural rigidity values are relatively similar despite the higher mass per unit area of laminate-2. Similar qualitative and quantitative observations showed the improved drapeability of laminate-7 compared to laminate-6. Based on hand-feel (qualitative comparison only), the drapeability of laminate-4 and laminate-5 was similar to laminate-2, while laminate-3 was even better. 10 The noise-producing characteristics of the laminates, when subjected to random folding and twisting motions, were compared via a subjective 5-point scale, where a value of 5 was assigned to the noisiest laminate and a value of 1 corresponds to a completely noiseless laminate. Laminates-1 and -6 (without dampening layer), laminates-2, -3, -4, -5, and -7 (with amorphous polymeric dampening 15 layers) and three commercial barrier laminates were compared by this method, and the results are shown in Table 3. Impak PAKVF4 is foil and polyethylene laminate with a thickness of about 110 microns. Valsem S165 is an aluminium foil and polyester laminate. Table 3. Laminate test sample Noise when flexed (5-point scale) Laminate-1 (no dampening layer) 4 Laminate-2 (polyurethane acrylate dampening layer) 2-3 Laminate-3 (epoxy dampening layer) 2 Laminate-4 (UV-cured epoxy-acrylate dampening layer) 3 Laminate-5 (thermoplastic polyurethane dampening layer) 3 Laminate-6 (no dampening layer) 4 Laminate-7(polyurethane acrylate dampening layer) 2-3 DEL35 5 Impak PAKVF4 4 Valsem S165 5 By comparison with undampened laminate-1 and laminate-6, it is apparent that the amorphous polymeric layers on each of laminate-2, laminate-3, laminate-4, laminate-5 and laminate-7 act as a sound-dampening layer to reduce the noise 5 emitted when flexing the laminate. These laminates are also much more silent barrier films than commercial foil laminates commonly used in battery and food applications. A quantitative test was also used to evaluate the noise-producing characteristics of selected laminates. The measurements were conducted in close accordance 10 with ISO 3747:2010. Thus, sound power data in the range of 100 to 10 kHz was measured in hemi-anechoic conditions when the laminates were subjected to random flexing. Samples 18cm wide were clamped in the test fixture and trimmed to the length of the frame (approx. 25cm). The frame imposes a fixed angle of twist in the laminate. The sample was held immobile along the top edge while the 15 bottom edge was excited with an electrodynamic shaker. The shaker mechanism was mounted underneath a reflective floor with the floor extending >1.2 m beyond the origin of measurement (hemi-anechoic conditions). The excitation was random (white noise), 50 Hz band-passed centred at 50 Hz with an amplitude (at the sample) of 4.6 Grms. The results of the measurements are shown in Table 4. Table 4. Laminate test sample (Overall / summed) Sound Power Linear (dB) A-weighted (dBA) Laminate-1 (no dampening layer) 72.6 72.0 Laminate-2 (polyurethane acrylate dampening layer) 66.4 63.9 DEL35 79.8 80.2 The results confirm the qualitative observations that (i) the amorphous polymeric layer acts as a sound-dampening layer to reduce the noise emitted when flexing the laminate (c.f. laminate-2 vs laminate-1), and (ii) the dampened laminates are much more silent barrier films than commercial foil laminates commonly used in battery and food applications (c.f. laminate-2 vs DEL35). Example 5. Enhancing the adhesion of the dampening layer to laminate-1. To prevent delamination in use, it is important that adjacent layers in the laminate layers, and particularly the dampening layer and the barrier layer, are strongly adhered. Three commercially available polyurethane-based primers, as shown in Table 5, were thus evaluated as candidates to compatibilize the polyester surface of laminate-1 with the polyurethane acrylate used to produce laminate-2. The polyurethane primers as supplied were dissolved or diluted in either tetrahydrofuran (THF) or acetone so that a thin (<1 g / m2) coating could be applied to the substrate. Lengths of 2-3 m of laminate-1 were then coated with these diluted compositions using a microfibre wiper (4mm nap). The primer coatings were air dried, with the required drying / curing time dependent on the primer system used. The thermoplastic polyester polyurethane primer (Estane S190A from Lubrizol) requires only solvent evaporation and drying is thus finished in minutes. Curing of Eraprime LV452 (from Era Polymers) and SikaBond TechGrip (from Sika) appears to involve both solvent evaporation and reaction of residual free isocyanate with atmospheric moisture, thus taking 30 minutes or several hours respectively. The primed laminate-1 films were then coated with a UV-cured polyurethane acrylate dampening layer by the method of Example 2, thus producing laminate-8, laminate-9 and laminate-10 as seen in Table 5. Adhesion was assessed semi-quantitively using a modification of ASTM D3359 5 (Standard Test Methods for Rating Adhesion by Tape Test). Using a new scalpel blade, a lattice comprising 4-5 parallel cuts in each direction was made in the amorphous polymeric coating on the substrate, a pressure-sensitive tape (3M 810D) was applied, firmly smoothed out over the lattice and then rapidly removed at 180°. Adhesion was evaluated by qualitatively assessing the degree of coating 10 removal. Minimal detachment of the coating was obtained relative to laminate-1, demonstrating a very significant improvement in adhesion of the polyurethane acrylate dampening layer to the BOPET surface when using each of the three primers. No significant effect of the very thin primer layers on laminate flexibility could be detected. 15 Table5. Laminate Primer Type Dilution 1 solvent Adhesion 1 none Poor 8 Estane S190A Thermoplastic polyester PU 0.5 - 2% (THF) Good 9 Eraprime LV452 45% solids - single component PU 10% (4.5% solids) (THF) Good 10 SikaBond TechGrip 100% solids - single component PU 2.5 - 5% (Acetone) Good Example 6. Preparation of electrodes A slurry was prepared by first dissolving a binder polyurethane (REFLEX 585A, available fromTownsend Chemicals) in dimethylformamide (DMF) (1 g in 60 ml) by continuous stirring at 50 °C for 2 hours until complete dissolution. Then conductive carbon black additive (CABOT LIX 200, 2 g) was added followed by homogenisation (Polytron, Kinematica, type PT 45 / 50, dial speed 3) for 1 hour, and probe sonication (Branson Digital Sonifier, model 450, BRANSON Ultrasonics Corporation (US)) for 1.25 hours at a 50 % amplitude (Factory-tuned 20 kHz ultrasonic design). The dispersion was kept cool during probe sonication. For the cathode precursor slurry, lithium iron phosphate (LiFePO4 or LFP) (17g) was then added to the mixture, followed by additional homogenisation for 30 minutes, and then additional probe sonication for a further 1.25 hours. For the anode precursor slurry, lithium titanate (Li4TisOi2 or LTO) (17g) was instead added to the mixture, followed by additional homogenisation for 30 minutes, and then additional probe sonication for a further 1.25 hours. As schematically represented in Figure 7, sheets of carbon cloth 702 (270 x 280 mm) (Avcarb HCB 1170, plain weave, electric resistivity 1.1x10 3 ohm-cm, 99.5% carbon content) were prepared with heat-activatable linear low density polyethylene (PE) tab seal strips 704 (one strip on each side of the carbon cloth) applied at the top and bottom. The tab seal strips were cut from a plastic shopping bag. The PE tab seals, which were about 100 pm thick and 10 mm wide (arrow 706), were positioned on carbon cloth 702 so as to provide terminal portions 708 with a width of 50 mm (arrow 710). The distance between the two PE strips (arrow 712) was 120 mm for LFP-coated electrodes and 130 mm for LTO-coated electrodes. The PE tab seals were then heat activated using a heat sealer to infiltrate the molten LLDPE into the weave of the carbon cloth. The carbon cloth was then held in place vertically using magnetic strips to support the cloth against a backing board and to mask the terminal portions and sprayed with an automatic spraying technique using one of the precursor electrode slurries. The spraying was conducted in a vertical direction at a flow rate of 115 ml / min, with the robot moving the spray nozzle from bottom to top at 5mm / sec when spraying with cathode precursor slurry containing LFP or at 6 mm / sec when spraying with anode precursor slurry containing LTO slurry. The stand-off distance between the nozzle tip and the fabric surface was 275 mm. Three passes were made on the first side, with an intermediate step of blowing hot air onto the coating after each pass (a hot air gun set at 250°C approximately 30 cm from the substrate, moving at the same speed as the spray arm). The same three-pass spray application was then used on the opposite side. The coated cloth was then dried in an oven at 70°C for one hour. Eight individual flexible electrodes were then cut from each coated cloth 702 using a hydraulic press, in a two x 4 array. The dimensions of the coated portion of the electrodes were 60 mm x 60 mm for the LFP-based cathodes and 65 mm x 65 mm for the LTO-based anodes, plus a tab portion of 30 mm length and 15 mm width. The electrodes had the geometrical configuration of electrodes 110, 112 depicted in Figure 2. Example 7. Development of the tab sealing methodology To provide electrical terminals for a flexible battery, it is necessary to provide conductive electrical conduits from the electrodes which pass through the flexible casing. A significant issue with many flexible battery designs is the vulnerability to air and moisture ingress or electrolyte leakage through the flexible casing at the location where these electrical connections pass through the casing. One approach is to use an uncoated terminal portion (a tab) of each electrode’s flexible current collector as the electrical conduit which protrudes through the sides of the flexible casing. In initial attempts to fabricate cells using carbon-cloth supported electrodes (of the type described in Example 6), the pouch was sealed by heat-sealing the aluminium laminate film directly onto the uncoated carbon cloth tabs of the electrodes. However, the resultant cells performed poorly in cycling tests and it was observed that the electrolyte was being lost. Further investigations revealed that the electrolyte was escaping the cell by wicking though the carbon cloth tabs, and it is believed that oxygen and moisture also entered the cell via the tab seal. To address this wicking issue, and also to better resist air / moisture ingress, it was proposed to infiltrate the fibres of the carbon cloth with a hydrophobic polymer at the location of heat sealing to the barrier film (i.e. where the tabs passed through the flexible casing). Heat-activatable linear low density polyethylene (PE) tab seal strips (85 pm thick and 10 mm wide; cut from a plastic shopping bag) were thus placed on either side of an AvCarb HCB 1170 carbon cloth and heat activated using a platinum press at 130-140 °C for 3-4 mins with a 60 pm shim (strip of stainless steel on each side to improve heat distribution). After cooling, strips of the carbon cloth (dimensions 80 mm x 20 mm) were cut, with the heat-activated activated tab seal located in the middle of the strips. The bottom half of a strip was then immersed in electrolyte (1:1 EC / DMC containing 1M LiTFSI) in a vial, with the top half dangling out of the vial. It was observed that electrolyte wicking was blocked by the activated PE tab seal. Carbon cloth strips produced in this manner were cut through the tab seal and imaged by scanning electron microscopy (SEM). The SEM images demonstrated that the heat-activated LLDPE has penetrated well though the weave of the carbon cloth, forming a good seal around the yarns, but not into the bundles of fibres in each yarn. Further development efforts were therefore conducted to improve the penetration. The total amount of heat-activated polymer was doubled by placing two PE tab seal strips on each side of the carbon cloth (4 x 85 pm thick in total). The PE tab seals were then subjected to an initial adhesion step using an impulse heat sealer for a short time, followed by a sustained heat-sealing step using a continuous heat sealer at 140 °C or 150 °C for periods of time ranging from 1 to 5 min. This was done by sandwiching the carbon cloth with adhered tab seals between two Teflon sheets and then two strips of stainless steel to keep it in place. The whole assembly was placed between the jaws of the continuous heat sealer for the desired time and temperature. The best sealing results were observed after 2 min of application at either 140 °C or 150 °C, where complete penetration of the PE within the woven structure and between the individual fibres in the yarns was obtained. In the low magnification SEM image shown in Figure 8, it can be seen that the heat-activated PE tab seal formed a cohesive polymer layer 802 completely surrounding and sealing the woven yarns 804. In the high magnification SEM image shown in Figure 9, it can be seen that the heat-activated PE has penetrated into the porosity of each yarn, surrounding the individual carbon fibre filaments. Example 8. Battery fabrication Pouch-cell type lithium-ion batteries were fabricated using laminate-3 for the flexible casing, electrodes of the type produced by the method of Example 6 (except with ethylene-vinyl acetate (EVA) polymer, 33% vinyl acetate, as the tab seal instead of LLDPE), with one LFP-based electrode as the cathode and one LTO-based electrode as the anode, and a lithium-containing electrolyte. To prepare the pouch-type flexible casings, one rectangular piece of the multilayer laminate was folded in half and heat sealed together opposite the fold by activating the polymeric seal layer using a heat sealer, thus providing a pouch with a dimension of approximately 90 mm x 90 mm. One of the electrodes was positioned in the pouch, spaced apart from the edges by about 10 mm. A microporous polyethylene flexible separator (Solupor membrane 3P07A from Lydall Performance Materials), slightly larger in size than the electrodes, was then placed on top of the electrode in the pouch and the other electrode was then placed on top of the separator. The uncoated carbon cloth tabs of the two electrodes, positioned apart from each other, extended through one opening of the pouch such that the heat-activated EVA tab seals were just inside the pouch opening and aligned with the edges of the multi-layer laminate. The opening through which the tabs extended was then heat sealed by applying the heat sealer on both sides of the pouch. The heat and pressure applied by the heat sealer resulted in heat-activation of the LLDPE polymeric layer of the laminate and thus heat-sealing of the pouch film laminate to the EVA tab seal (which was already infiltrated through the weave of the carbon cloth). Thus, after cooling and re-solidification of the heat-activated adhesives, the pouch was hermetically sealed against air or moisture ingress or electrolyte escape via the carbon cloth tabs. The pouch was then moved to the antechamber of a glovebox and kept there under vacuum at 70 °C overnight to remove traces of moisture. The electrolyte (3.5 ml of 1:1 ethylene carbonate (EC) / dimethyl carbonate (DMC) containing 1M lithium bis(trifluoromethane)sulfonimide (LiTFSI)) was then added to the pouch cell, via the remaining opening, inside the glovebox, making sure to wet both sides of the electrodes. The pouch was then placed into a vacuum sealing machine and de-gassed three times to infiltrate the electrolyte into the pores of the electroactive coating and the fabric current collector. The final opening of the pouch was then sealed in the glovebox using a vacuum heat sealer. The resultant lithium-ion batteries had the configuration of flexible electrochemical energy storage device 100 as described herein with reference to Figures 1 and 2. Example 9. Cycling performance of the battery Battery testing results were obtained for a lithium-ion battery as prepared in Example 8. The cycling tests were performed on a MACCOR battery tester series 4000. A C / 10 current rate was used, with a potential window from 1.0 to 2.6 V. Excellent cycling performance was obtained, with an initial areal capacity of above 2.2 mAh / cm2 and more than 90% capacity retention after 36 cycles. Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention. Future patent applications may be filed on the basis of or claiming priority from the present application. It is to be understood that the following provisional claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to 5 or omitted from the claims at a later date so as to further define or re-define the invention or inventions.

Claims

1. A flexible electrochemical energy storage device comprising at least two separated electrodes 110,112 and an electrolyte 120 contained within a flexible casing 118 having an inside surface facing the electrolyte 120, wherein the flexible casing 118 comprises a multi-layer lam inate 132,134, 300, 500 comprising:a polymeric seal layer 316, 516 at the inside surface of the flexible casing 118, wherein the polymeric seal layer is chemically inert to the electrolyte 120;a barrier layer 308,508 comprising a semi-crystalline polymeric film 310,510 and a water-impervious metallic or inorganic film 312,512; anda dampening layer 318,518 comprising a substantially amorphous polymer with a Tg below 35°C,wherein the dampening layer 318, 518 dampens sound produced when flexing the flexible casing 118.

2. The flexible electrochemical energy storage device of claim 1, wherein the dampening layer 318,518 has a thickness of between 10 pm and 200 pm, preferably between 30 pm and 100 pm.

3. The flexible electrochemical energy storage device of claim 1 or claim 2, wherein the substantially amorphous polymer has a Tg below 30°C, preferably below 25°C.

4. The flexible electrochemical energy storage device of any one of claims 1 to 3, wherein the substantially amorphous polymer is selected from the group consisting of an acrylate polymer, an epoxy polymer, a mixed acrylate-epoxy polymer, a silicone polymer, a plastisol and a thermoplastic polymer.

5. The flexible electrochemical energy storage device of claim 4, wherein:the acrylate polymer is a polymer of (i) at least one selected from the group consisting of a urethane di- or poly(meth)acrylate, a polyalkylene oxide-linked di- or poly(meth)acrylate, a (meth)acrylated epoxidized triglyceride, and (ii) optionally a reactive diluent;the epoxy polymer is a polymer of at least one selected from the group consisting of a bisphenol epoxy resin and an aliphatic epoxy resin;the mixed acrylate-epoxy polymer is a polymer of (i) one or more selected from the group consisting of a urethane di- or poly(meth)acrylate, a polyalkylene oxide-linked di- or poly(meth)acrylate, a (meth)acrylated epoxidized triglyceride, (ii) one or more selected from the group consisting of a bisphenol epoxy resin and an aliphatic epoxy resin, and (iii) optionally a reactive diluent; andthe thermoplastic polymer is selected from the group consisting of a polyurethane, poly(styrene-butadiene-styrene) (SBS) and poly(styrene-ethylene-butylene-styrene) (SEBS).

6. The flexible electrochemical energy storage device of any one of claims 1 to 5, wherein the dampening layer 318, 518 is positioned between the barrier layer 308, 508 and an outside surface of the flexible casing 118, preferably wherein the dampening layer 318, 518 is at the outside surface of the flexible casing.

7. The flexible electrochemical energy storage device of any one of claims 1 to 6, wherein the polymeric seal layer 316, 516 is present on the entire inside surface of the flexible casing 118.

8. The flexible electrochemical energy storage device of any one of claims 1 to 7, wherein the flexible casing 118 is hermetically sealed along at least a portion of its periphery by a seal formed by the polymeric seal layer 316, 516,preferably wherein the seal hermetically seals two portions of multi-layer laminate 132, 134, 300, 500 together.

9. The flexible electrochemical energy storage device of any one of claims 1 to 8, wherein the polymeric seal layer 316, 516 comprises a heat-activatable adhesive polymer, preferably selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, acid modified polyethylene or polypropylene, acid copolymers of polyethylene or polypropylene and ethylene-vinyl acid copolymers.

10. The flexible electrochemical energy storage device of any one of claims 1 to 9, wherein the semi-crystalline polymeric film is a biaxially-oriented polymeric film.

11. The flexible electrochemical energy storage device of any one of claims 1 to 10, wherein the semi-crystalline polymeric film 310, 510 has a thickness of less than about 20 pm, preferably between 5 pm and 15 pm.

12. The flexible electrochemical energy storage device of any one of claims 1 to 11, wherein the semi-crystalline polymeric film comprises a polymer selected from the group consisting of a polyester, a polyolefin and a polyamide.

13. The flexible electrochemical energy storage device of claim 12, wherein the polyester is selected from polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), the polyolefin is selected from polypropylene and polyethylene, and the polyamide comprises at least one selected from polyamide 6 (polycaprolactam), polyamide 66 (polyhexamethylene adipamide), polyamide 610 and polyamide-MXDX (polyxylylene adipamide).

14. The flexible electrochemical energy storage device of any one of claims 1 to 13, wherein the semi-crystalline polymeric film is a biaxially orientedpolypropylene (BOPP) film or a biaxially oriented polyethylene terephthalate (BOPET) film.

15. The flexible electrochemical energy storage device of any one of claims 1 to 14, wherein the water-impervious metallic or inorganic film 312, 512 is a coating on the semi-crystalline polymeric film.

16. The flexible electrochemical energy storage device of claim 15, wherein the coating is produced on the semi-crystalline polymeric film by vapor deposition, and preferably by a vapor deposition technique selected from vacuum deposition, electron beam deposition and plasma enhanced chemical vapour deposition.

17. The flexible electrochemical energy storage device of claim 15 or claim 16, wherein the coating has a thickness of less than about 100nm, such as between 20nm and 70nm.

18. The flexible electrochemical energy storage device of any one of claims 1 to 17, wherein the water-impervious metallic or inorganic film 310, 510 is selected from the group consisting of (i) a metallic film comprising aluminium, (ii) an oxide film selected from aluminium oxide, tin oxide, silicon oxide and mixtures thereof, and (iii) a nitride film selected from aluminium nitride, silicon nitride and mixtures thereof.

19. The flexible electrochemical energy storage device of any one of claims 1 to 18, wherein the multi-layer laminate 132, 134, 300, 500 comprises one or more further barrier layers 308, 508, each further barrier layer comprising a semi-crystalline polymeric film and a water-impervious metallic or inorganic film.

20. The flexible electrochemical energy storage device of claim 19, wherein the barrier layer 308, 508 and at least one further barrier layer are adhered together by an adhesive interlayer 314, 514, preferably with their respective water-impervious metallic or inorganic films 312, 512 facing each other.21 .The flexible electrochemical energy storage device of any one of claims 1 to 20, wherein the dampening layer 318, 518 is adhered to the barrier layer 308, 508.

22. The flexible electrochemical energy storage device of claim 21, wherein the dampening layer 318, 518 is adhered to the semi-crystalline polymeric film 310, 510 of the barrier layer 308. 508.

23. The flexible electrochemical energy storage device of claim 22, wherein the semi-crystalline polymeric film 310, 510 of the barrier layer 308, 508 is surface-activated, preferably by a method selected from corona discharge treatment, plasma treatment, flame treatment and dielectric barrier discharge treatment, to enhance adhesion of the dampening layer to the barrier layer.

24. The flexible electrochemical energy storage device of any one of claims 21 to 23, wherein the barrier layer 308, 508 is primed with a primer composition, preferably in an amount of less than 2g / m2, to enhance adhesion of the dampening layer to the barrier layer.

25. The flexible electrochemical energy storage device of any one of claims 1 to 24, wherein the multi-layer laminate 132, 134, 300, 500 has a water vapour transmission rate of less than 200 mg / m2 / day, preferably less than 100 mg / m2 / day, as measured by ASTM F3299-18.

26. The flexible electrochemical energy storage device of any one of claims 1 to 25, wherein a specimen comprising two laminated sheets of the multi-layerlaminate 132, 134, 300, 500 has a flexural rigidity of less than 3000 pN.m, preferably less than 2000 pN.mm, most preferably less than 2000 pN.m, as measured by AS 2001.2.9.

27. The flexible electrochemical energy storage device of any one of claims 1 to 26, wherein the flexible casing 118 is in the form of a planar pouch formed from one or more sheets of the multi-layer laminate 132, 134, 300, 500.

28. The flexible electrochemical energy storage device of any one of claims 1 to 27, wherein each electrode 110, 112 comprises a flexible current collector 122, 126, preferably a fabric current collector.

29. The flexible electrochemical energy storage device of any claim 28, wherein the flexible current collector 122, 126 is an electrically conductive woven fabric current collector and the flexible current collector comprises a terminal portion of the woven fabric which passes through the flexible casing to provide an electrical terminal for the flexible lithium-ion battery, wherein the flexible casing 118 is sealed against ingress of air or egress of the electrolyte 120 where the terminal portion passes through the flexible casing by a polymeric sealant infiltrated through the weave of the woven fabric.

30. The flexible electrochemical energy storage device of claim 29, wherein the polymeric sealant is a heat-activated thermoplastic.31 .The flexible electrochemical energy storage device of claim 30, wherein the heat-activated thermoplastic is a polyolefin, preferably a polyethylene, most preferably linear low density polyethylene.

32. The flexible electrochemical energy storage device of any one of claims 28 to 31, wherein each electrode 110, 112 comprises an electroactive composition supported on the flexible current collector 122, 126, the electroactivecomposition comprising an anode or cathode material, a polymeric binder and optionally a conductive additive.

33. The flexible electrochemical energy storage device of any one of claims 1 to 32, which is a lithium-ion secondary battery.

34. A method of producing a flexible electrochemical energy storage device, the method comprising:(i) providing a flexible multi-layer laminate 132, 134, 300, 500 comprising:a polymeric seal layer 316, 516 at one surface of the multi-layer laminate 132, 134, 300, 500;a barrier layer 308, 508 comprising a semi-crystalline polymeric film 310, 510 and a water-impervious metallic or inorganic film 312, 512; anda dampening layer 318 comprising a substantially amorphous polymer with a Tg below 35°C;(ii) producing a flexible casing 118 from the multi-layer laminate 132, 134, 300, 500, wherein the polymeric seal layer 316, 516 is located at an inside surface of the flexible casing 118;(iii) functionally arranging at least two separated electrodes 110, 112 and an electrolyte 120 within the flexible casing 118; and(iv) hermetically sealing the flexible casing 118.

35. The method of claim 34, wherein (i) providing the multi-layer laminate 132, 134, 300, 500 comprises coating the barrier layer 308, 508 with a coating composition and curing and / or drying the coating composition to form the dampening layer 318, 518 adhered to the barrier layer 308, 508.

36. The method of claim 35, wherein the barrier layer 308, 508 is coated in a roll-to-roll coating process.

37. The method of claim 35 or claim 36, further comprising priming the barrier layer with a primer composition, before coating the barrier layer 308, 508 with the coating composition, to enhance adhesion of the dampening layer 318, 518 to the barrier layer 308, 508.

38. The method of any one of claims 34 to 37, wherein (i) providing the multilayer laminate 132, 134, 300, 500 comprises laminating the barrier layer to one or more further barrier layers, each further barrier layer comprising a semi-crystalline polymeric film 310, 510 and a water-impervious metallic or inorganic film 312, 512, by one or more adhesive interlayers, preferably wherein the barrier layer 308, 508 and one further barrier layer are adhered together with their respective water-impervious metallic or inorganic films facing each other.

39. The method of any one of claims 34 to 38, wherein (i) providing the multilayer laminate 132, 134, 300, 500 comprises laminating the polymeric seal layer 316, 516 to the barrier layer with one or more adhesive interlayers.

40. A flexible article of manufacture comprising the flexible electrochemical energy storage device of any one of claims 1 to 33.41 .The flexible article of manufacture of claim 40, wherein the flexible electrochemical energy storage device is integrated into a flexible fabric portion of the flexible article of manufacture.

42. A garment comprising the flexible article of manufacture of claim 40 or claim 41.

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