GB2574804A

GB2574804A - Battery, battery cell, cell module and related methods

Info

Publication number: GB2574804A
Application number: GB201809557A
Authority: GB
Inventors: Claire O'Sullivan Melanie; Blincow Jack
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2018-06-11
Filing date: 2018-06-11
Publication date: 2019-12-25
Also published as: GB201809557D0; GB2574804A8

Abstract

A flexible battery 1 comprises a stack of electrochemical cells 2, each cell being movable relative to an adjacent cell when the battery is bent. An insulating layer is preferably provided between each cell, and may comprise a pouch in which the anode, cathode, anode and cathode current collectors and separator are located, the pouch forming the insulating layer. In a further aspect, an electrochemical cell suitable for a flexible battery, comprises an anode, anode current collector, cathode, cathode current collector and separator, all located within a pouch, wherein anode and cathode cell lead-outs extend from the pouch and are attached to an external surface of the pouch to form respective anode and cathode battery lead-out pockets. Also disclosed is a cell module including this cell, a method of forming the flexible battery, a method of forming the electrochemical cell for a flexible battery and a method of forming the cell module.

Description

Battery, Battery Cell, Cell Module and Related Methods

Field of the Invention

The present invention relates to a flexible battery, to an electrochemical cell for a flexible battery, to a cell module, to a method of forming a flexible battery, to a method of forming an electrochemical cell for a flexible battery and to a method of forming a cell module.

Background of the Invention

A battery can be provided with a relatively high charge capacity by increasing the number of active material layers in a multi-electrode stack. However, increasing the number of active material layers also increases the thickness of the multi-layered electrodes and the resulting battery, which reduces its flexibility.

A thicker, high capacity, battery having a high degree of flexibility is desirable, particularly for wearable technology applications.

It is an object of the invention to provide a flexible battery, to an electrochemical cell for a flexible battery, to a cell module, to a method of forming a flexible battery, to a method of forming an electrochemical cell for a flexible battery and to a method of forming a cell module.

Summary of the Invention

The present inventors have found that by allowing the constituent cells of a battery to move relative to one another, it is possible to produce a relatively thick battery that retains a high level of flexibility that works in both straight and bent configurations with little or no degradation in performance. Electrochemical cells can be connected in series or in parallel to increase the corresponding battery voltage or charge capacity, respectively. By engineering the electrochemical cells so that they can move relative to each other, displace, or slide past one another, a modular battery may be realised that while thick, retains the flexibility of an individual cell. This modular approach enables battery parameters such as voltage, charge capacity, peak pulse power and thickness to be easily tailored to suit an individual application by changing the number and type of cells in the battery, without substantially altering the flexibility of the battery.

Accordingly, in a first aspect there is provided a battery comprising a stack of electrochemical cells, each cell being movable relative to an adjacent cell when the battery is bent.

The battery may comprise an insulating layer. The insulating layer may be positioned between each cell. The insulating layer may be a single layer, separate to either cell or, each cell may have its own insulating layer. The insulating layer can be formed from Polyethylene terephthalate (PET), and can be applied to the external surfaces of the current collectors of each cell.

The insulating layer may be formed from, or coated with, a material to enable adjacent cells to move relative to each other.

In a preferred embodiment, the battery comprises a flexible external package and the stack of electrochemical cells is received in said flexible external package.

The flexible external package may be formed from an elastic material.

The flexible external package and the outermost cells of the stack are preferably movable relative to each other.

An inner surface of the flexible external package can be covered with a material that allows the outermost cells and the flexible external package to move relative to each other.

In a preferred embodiment, each electrochemical cell contains an anode, a cathode; a separator between the anode and the cathode; an anode current collector; and a cathode current collector. Each cell may comprise a pouch encapsulating the anode, the cathode, the separator between the anode and the cathode, the anode current collector and the cathode current collector. In this instance, the insulating layer may be formed by the pouch or a layer of the pouch.

An anode cell lead-out may extend from the anode current collector out of the pouch and, a cathode cell lead-out may extend from the cathode current collector out of the pouch.

Optionally, the anode cell-lead out is integral with the anode current collector, and the cathode cell lead-out is integral with the cathode current collector.

Preferably, the anode cell lead-outs of the electrochemical cells are directly connected to each other, and the cathode cell lead-outs of the electrochemical cells are directly connected to each other.

In another embodiment, the battery comprises an anode battery lead-out extending from, and in electrical connection with, each anode cell lead-out, and a cathode battery lead-out extending from, and in electrical connection with, each cathode cell lead-out, so that each cell, together with its anode and cathode battery lead-outs, forms a cell module.

The anode cell lead-out and the anode battery lead-out of each cell module may be movable relative to each other. Similarly, the cathode cell lead-out and the cathode battery lead-out of each cell module may be movable relative to each other.

Each cell module preferably comprises an anode battery lead-out pocket to slideably receive the anode battery lead-out, and a cathode battery lead-out pocket to slideably receive the cathode battery lead-out.

The anode battery lead-out pocket may be formed between the anode cell lead-out and a first external surface of the pouch, and the cathode battery lead-out pocket may be formed between the cathode cell lead-out and a second external surface of the pouch opposite to said first external surface.

Preferably, the anode cell lead-out is attached to the first external surface, and the cathode cell lead-out is attached to the second external surface.

Some embodiments may comprise an insulating layer, such as adhesive tape, extending over said anode cell lead-out that attaches said anode cell lead-out to said first external surface such that an opening is formed along an edge of the anode cell lead out to provide access to the anode battery lead-out pocket. An innsulating layer, such as adhesive tape, may also extend over said cathode cell lead-out that attaches said cathode cell lead-out to said second external surface such that an opening is formed along an edge of the cathode cell lead-out to provide access to the cathode battery lead-out pocket.

An end of each of the anode and cathode battery lead-outs may be received in respective anode and cathode battery lead-out pockets to extend therefrom.

The end of each of the anode and cathode battery lead-outs can be folded back on itself to form a double layer within the anode and cathode lead-out pockets, respectively.

A resiliently deformable material may be received in the fold between said double layer of respective anode and cathode battery lead-outs.

In a preferred embodiment, the deformable material may be a conductive material, such as stainless steel wool, received in the fold between said double layer of respective anode and cathode battery lead-outs so as to protrude therefrom.

The anode and cathode battery lead-out pockets of each cell module may each be configured so that the anode battery lead-out extends laterally from said anode battery lead-out pocket in one direction, and the cathode battery lead-out extends laterally from said cathode battery lead-out pocket in the opposite direction.

Preferably, the cell modules are arranged such that the anode battery lead-out pocket of one cell faces the anode battery lead out pocket of an adjacent cell such that the anode battery lead-outs of all the cells extend in the same direction, and such that the cathode battery leadout pocket of one cell faces the cathode battery lead-out pocket of an adjacent cell such that the cathode battery lead-outs of all the cells extend in the same direction.

The direction in which the anode battery lead-outs extend may be laterally opposite to the direction in which the cathode battery lead-outs extend.

All the anode battery lead-outs can be electrically connected to each other at their free ends remote from said anode battery lead-out pockets, and all the cathode battery lead-outs can be electrically connected to each other at their free ends remote from said cathode battery leadout pockets.

According to another aspect of the invention, there is provided an electrochemical cell for a battery comprising a pouch having first and second opposing external surfaces, the pouch containing an anode, a cathode; a separator between the anode and the cathode; an anode current collector; and a cathode current collector, wherein an anode cell lead-out extends from the pouch and is attached to said first external surface to form an anode battery lead-out pocket, and a cathode cell lead-out extends from the pouch and is attached to said second external surface to form a cathode battery lead-out pocket.

The anode cell lead-out may be integrally formed with the anode current collector, and the cathode cell lead-out may be integrally formed with the cathode current collector. The use of the term ‘integral’ should be taken to include embodiments in which respective cell lead-outs and their current collectors are formed as a unitary component. However, it also includes embodiments in which the cell lead-outs and their respective current collectors are separately formed but joined together in some way during assembly, such as by welding or gluing.

According to another aspect of the invention, there is provided a cell module comprising the cell according to the invention, and an anode battery lead-out slideably received in the anode battery lead-out pocket, and a cathode battery lead-out slideably received in the cathode battery lead-out pocket.

An end of each of the anode and cathode battery lead-outs received in respective anode and cathode battery lead-out pockets may be folded back on itself to form a double layer.

A resiliently deformable material may be received in the fold between said double layer.

According to another aspect of the invention, there is provided a method of forming a flexible battery comprising a stack of electrically connected electrochemical cells, the method comprising stacking the cells such that each cell can move relative to an adjacent cell when the battery is bent.

Each cell may be separated from an adjacent cell by an insulating layer that enables the cells to move relative to each other. The insulating layer may form part of a pouch that encapsulates the cell. The method can include inserting the plurality of electrochemical cells into a flexible external package.

According to another aspect of the invention, there is provided a method of forming an electrochemical cell for a flexible battery comprising inserting an anode , a cathode; a separator between the anode and the cathode; an anode current collector; and a cathode current collector, into a pouch having first and second opposing external surfaces, and such that anode and cathode cell lead-outs extend from the pouch, attaching said anode cell leadout to the first external surface to form an anode battery lead-out pocket, and attaching said cathode cell lead-out to the second external surface to form a cathode battery lead-out pocket.

According to another aspect of the invention, there is provided a method of forming a cell module according to the invention, comprising inserting an anode cell battery lead-out into the anode battery lead-out pocket of a cell according to the invention, and inserting a cathode cell battery lead-out into the cathode battery lead-out pocket of the cell according to the invention.

The method of forming a cell module may include folding an end of each of the anode and cathode cell battery lead-outs prior to insertion of said ends into respective anode and cathode battery lead-out pockets.

The method may also include placing a resiliently deformable material into the fold of the anode and cathode battery cell lead-outs prior to insertion of the anode and cathode battery cell lead-outs into respective anode and cathode battery lead-out pockets.

Batteries as described anywhere herein are preferably rechargeable batteries.

Description of the Drawings

The invention will now be described in more detail with reference to the drawings in which:

Figure 1 illustrates a schematic of an individual polymer battery cell in which each of the anode and cathode is a multilayer electrode, which may be used to form a flexible battery according to an embodiment of the invention;

Figure 2 illustrates a schematic of another individual flexible polymer battery cell in which each of the anode and cathode is a single layer, and which may be used to form a flexible battery according to an embodiment of the invention;

Figures 3A illustrates a schematic of a flexible polymer battery in exploded form, according to an embodiment of the invention;

Figure 3B illustrates the flexible polymer battery of Figure 3 A in assembled form;

Figure 3C illustrates the steps involved in the assembly of the flexible polymer battery of Figures 3A and 3B;

Figure 4 is an exploded schematic view of a flexible polymer battery according to another embodiment of the invention;

Figure 5A is a perspective view of an assembled flexible polymer battery, such as the polymer battery shown in Figure 4, in a flat configuration;

Figure 5B is an end view of the assembled flexible polymer battery of Figure 5A, in a bent configuration;

Figures 6A to 6G shows a series of steps involved in the formation of an individual polymer battery cell for use in the flexible polymer battery according to Figure 4;

Figure 7A to 7C shows a series of steps to illustrate how the battery lead-outs are formed;

Figure 8A to 8F shows a series of steps to illustrate how alternative battery lead-outs are formed;

Figures 9A to 9F shows a series of steps involved in assembling the cells of Figure 6A to 6G into a flexible polymer battery according to an embodiment of the invention, using battery lead-outs formed as shown in either Figures 7A to 7C or 8A to 8F;

Figures 10A to 10E shows a series of steps to illustrate how the flexible polymer battery is encapsulated in a flexible external package;

Figures 11A to 11G show the steps involved in fabricating a battery according to the embodiment of Figure 3;

Figures 12A and 12B are battery discharge curves for a flexible polymer battery according to an embodiment of the invention as shown in Figure 4 and which uses cells the same, or similar to, that shown in Figure 1, in a flat and bent configuration, respectively;

Figures 13A and 13B are battery discharge curves for a flexible polymer battery according to an embodiment of the invention as shown in Figure 4 and which uses cells the same, or similar to, that shown in Figure 2, in a flat and bent configuration, respectively;

Figures 14A and 14B are graphs to show the effect of battery conformation on midpoint voltage, and on battery charge capacity, respectively;

Figure 15A to E shows a sequence of steps involved in the formation of another embodiment of an individual cell, a plurality of which may be incorporated into a flexible battery according to an embodiment of the invention;

Figure 16A to 16G shows a sequence of steps involved in the formation of another embodiment of an individual cell, a plurality of which may be incorporated into a flexible battery according to an embodiment of the invention; and

Figure 17 shows a schematic view of a flexible battery assembled from four of the cells assembled according to Figures 16A to 16G.

Detailed Description of the Invention

Embodiments of the invention will primarily described with reference to polymer batteries. The use of a conjugated polymer in the anode or cathode of a polymer-based battery cell is disclosed in, for example, Journal of Power Sources, Volume 177, Issue 1, 15 February 2008, Pages 199-204, in Chem. Rev. 2016, 116, 9438-9484 and in Chemical Reviews, 1997, Vol. 97, No. 1 209. However, embodiments of the invention are applicable to other battery types. For example, embodiments of the invention are also applicable to lithium-ion type batteries as disclosed in, for example, Energy Environ. Sci., 2014, 7, 1307; Adv. Mater. Technol. 2018, 1700375; Lithium-air batteries, as disclosed in Energy Environ. Sci., 2017, 10, 2056; Zinc-air batteries, as disclosed in Energy Environ. Sci., 2017, 10, 2056, Zinc-manganese batteries, Nickel-metal hydride batteries and Nickel-iron batteries.

A polymer battery 1, according to one embodiment of the invention, is shown in Figure 3A and 3B. A second embodiment is shown in Figures 4 and 5. Each embodiment comprises a plurality of electrochemical cells 2 in stacked relation. The cells 2 are configured so that they can move or displace relative to each other to allow the battery 1 to fold. Prior to describing the polymer battery 1, reference will first be made to the individual cells 2 of Figures 1 and 2.

With reference to Figure 1, there is shown a schematic of a vacuum sealed individual electrochemical cell 2 containing a plurality of anode layers and a plurality of cathode layers, a plurality of which cells 2 can be used in the formation of a battery 1 according to an embodiment of the invention.

The cell 2 has a multilayer composite electrode consisting of an active material impregnated stainless steel (AM/SS) layer 3 and two free-standing active material layer films (AM) 4 with a thin layer of gel electrolyte 5 between each of the layers 4. In other embodiments, the impregnated stainless steel layer and / or the gel electrolyte layers may be absent. If the gel electrolyte layer is absent, a liquid electrolyte may be located between active material films, e.g. an ionic liquid, an inorganic or organic salt dissolved in a solvent.

The active material of the cathode is F8-TFB and the active material of the anode is F8BT, although it will be appreciated that these polymers may be replaced with other electrochemically active polymers.

F8-TFB

F8BT

The separator S consists of a nylon mesh impregnated with gel electrolyte. However, the separator S may be selected from separators known to the skilled person and may comprises a gel comprising an electrolyte solution or a liquid electrolyte. The separator S may be a solid polymer electrolyte.

Aluminium foil is used for the current collectors 6a,6c. However, the anode and cathode current collectors 6a,6c may each independently comprise or consist of a layer of another conductive material, for example a metal such as copper instead of aluminium; a conductive organic polymer such as poly(ethylene dioxythiophene) or polyaniline; or an inorganic conductive compound such as a conductive metal oxide, for example indium tin oxide.

The whole cell 2 is sealed in a vacuum pouch 8 to provide good inter-layer contact and prevent ingress of oxygen or moisture. A cell 2 of this structure can be expected to have an _2 areal capacity of 0.11 mAh cm’ when discharged to 1,5V.

With reference to Figure 2, there is shown a schematic of another vacuum sealed individual electrochemical cell 2.

The anode 4a and cathode 4c are each a single layer electrode. The anode 4a of the individual electrochemical cell 2 of Figure 2 consists of a blend of Schiff Base Polymer 1, conductive carbon, ionic liquid (BMP-TFSI) and sodium alginate as binder; the cathode 4c replaces Schiff Base Polymer 1 with Polytriphenylamine 1.

Schiff Base Polymer 1

Polytriphenylamine 1

The separator S consists of an oven dried filter paper impregnated with ionic liquid. Al/PET is used as the current collector 6a,6c, with the active area defined by an insulating SU-8 (photoresist) layer. The whole cell 2 is sealed in a vacuum pouch 8 to provide good interlayer contact and prevent ingress of oxygen or moisture. A cell 2 of this structure is expected _2 to have an areal capacity of approximately 0.32 mAh cm’ when discharged to 1.5V.

It will be appreciated that the separator S is not limited to an oven dried filter paper impregnated with ionic liquid. Furthermore, the active area does not necessarily need to be SU-8. For example, any insulating layer that shows good adhesion to the current collector, is electrically insulating, is flexible, can be rendered hydrophobic with SF6 plasma treatment, and is chemically resistant to ionic liquid may be used.

Similarly deposition of this layer is not limited to photolithographic patterning, but could also be achieved by reel-to-reel lamination of a patterned film, printing methods e.g. screen printing, dispense printing, gravure printing etc. including or excluding a curing step e.g. thermal, UV etc.

Figure 3A illustrates an exploded perspective schematic view of a flexible polymer battery 1 having three cells 2, each of which may be either of the cells 2 described above with reference to Figures 1 or 2. Figure 3B illustrates the battery of Figure 3A in assembled form, and Figure 3C illustrates a sequence of steps to be followed in the assembly of the battery shown in Figures 3A and 3B.

In the embodiment of Figure 3A and 3B, anode cell lead-outs 7a from each cell 2 are connected directly to one another, and the cathode cell lead-outs 7c are connected directly to one another, so no battery lead-outs are required to connect the respective anode and cathode cell lead-outs 7a,7c together. Good electrical connection between cells 2 is assured as a result of this direct connection and the design is simple.

With reference to Figure 3C, it will be understood that each cell 2 is attached to an adjacent cell 2 at a region 2a extending along one edge, i.e. the edge from which the cell lead-outs 7a,7b extend. Other than at this region 2a, the cells 2 remain physically unconnected to each other, allowing the cells 2 to displace relative to one another when the battery 1 is bent, and with the connected regions 2a remaining fixed to each other. This type of displacement is similar to that experienced when a stack of Post-it® notes, or a paperback book, is bent about an axis extending parallel to the connected edge or spine, and if each sheet of paper in the stack is considered to represent an individual cell 2. Thus, the battery 1 has a high degree of flexibility. As the pouches 8 of adjacent cells 2 are in contact, relative movement between the cells 2 is improved by using a low-friction material for the pouches 8 or by coating the pouches 8 with such a material. For example, the pouches 8 may be formed from polyethylene or Teflon foil. Alternatively, or in addition, the pouches may be coated with a lubricant such as paraffin or silicone oil.

With further reference to Figure 3C, it will be seen that each cell 2 (as shown in Figure 3C(i)), together with its integral cell lead-outs 7a,7c, initially has a strip of adhesive applied to the edge region 2a of one or both sides of each cell 2 so that the cells 2 adhere to each other at said region 2a when stacked, as shown in Figure 3C(iii). Once all the anode cell-lead outs 7a have been electrically connected to each other, and all the cathode cell lead-outs 7c have been electrically connected to each other, the stacked cells 2 are encapsulated in the flexible outer package 9 as described in more detail below, with reference to Figures 3A and 3B, and as shown in Figure 3C(iv). It will be appreciated that the cells 2 may also be attached to each other at the edge region by means other than by the use of adhesive.

Although the cells 2 are described and illustrated with reference to an individual pouch 8, it will be understood that each individual cell 2 need not be entirely encapsulated and that each cell 2 may instead be separated by an insulating layer that separates each cell 2 from an adjacent cell 2. The insulating layer 8 may be formed from a lubricious material or be coated with a lubricant to enable the cells 2 to move relative to each other. In embodiments having a pouch 8, the insulating layer may be formed by the pouch 8.

The cells 2 are contained, in their stacked formation, within an external package 9. A flexible adhesive bandage can be used. However, the external package 9 preferably has elastic properties so that it stretches as the battery 1 is bent. An elastic external package may be formed from, for example, acrylonitrile butadiene rubber and can have two layers 9a, 9b.

The inside surface of each layer 9a, 9b of the external packaging 9 may be coated with PTFE or another low-friction material layer 10, so that the outermost cells 2, or the pouches 8, or insulating layers, of the outermost cells 2, slide easily relative to the inner surface of the external packaging 9 with which they are in contact.

As the lead-outs 7a,7c are parallel to the x-axis, cell displacement occurs in the x-direction, giving high flexibility in the xz-plane, but limited flexibility in the yz-plane. The battery 1 is also rectangular in the xy-plane to encourage bending in the xz-plane, where x is the longest dimension of the battery 1. As the cell lead-outs 7 a,7c are directly connected, displacement of the cells 2 in the y-direction is prevented, and so reliance on the external package 9 to prevent displacement in the y-direction is not required.

An exploded-view of another embodiment of a polymer battery 1 according to the invention is shown in Figure 4. As shown, the battery 1 has three electrochemical cells 2, such as those described above with reference to Figures 1 or 2, which are vertically stacked and connected in parallel by battery lead-outs Ila, 11c which are separate to, but extend from, respective cell-lead outs 7a, 7c of each cell 2. The battery lead-outs Ila, 11c are secured to the battery external packaging 9 and are immobile relative thereto. The battery external packaging 9 is flexible, but may also have elastic properties so that it stretches as the battery 1 is bent and holds the internal electrochemical cells 2 closely together when the battery 1 has a flat conformation. As indicated above, the individual cells 2 include discrete pouches 8 so that each cell 2 can slide relative to its adjacent cell 2 when the battery 1 is bent.

The inside surface of the battery external packaging 9 may have a low friction coefficient to enable the cells 2 to slide freely along its surface. This can be achieved by applying Teflon, or other low-friction coating, to the inner surface of each layer 9a, 9b the packaging 9.

Figure 5A shows a perspective view of an assembled flexible polymer battery 1, such as the polymer battery 1 shown in Figure 4, in a flat configuration. As indicated previously, the surface of the battery 1 in the xy-plane is rectangular to encourage bending in the xz-plane, where x is the longest dimension. The cells 2 can freely slide in the x-direction, to give high flexibility in the xz-plane, as demonstrated by Figure 5B, which shows an end view of the assembled flexible polymer battery 1 of Figure 4 and Figure 5A, in a bent configuration.

To prevent displacement of the cells 2 in the y-direction, and the risk of the battery 1 shorting, the edges of the battery external packaging 9 can be tightly sealed against the edge of the cells 2. As the cells 2 cannot displace in the y-direction, flexibility of the battery 1 is limited in the yz-plane.

As indicated above, in the embodiment of Figures 4 and 5, separate anode and cathode battery lead-outs Ila, 11c, extend from respective anode and cathode cell lead-outs 7a, 7c of each cell 2. Each battery lead-out Ila, 11c can slide relative to its corresponding cell lead-out 7a, 7c, from which it extends, to accommodate flexing of the battery 1 as the cells 2 slide over each other.

Each of the anode and cathode cell lead-outs 7a, 7c from a cell 2 extend from the pouch 8 of that cell 2. The anode cell lead-out 7a is folded onto a first external surface of the pouch 8, and the cathode cell lead-out 7c is folded onto a second, opposing, external surface of the pouch 8. As described in more detail below, with reference to Figure 9A to 9F, the anode cell lead-out 7a is attached to the first surface so as to form an anode battery lead-out pocket together with the first external surface. Similarly, the cathode cell lead-out is attached to the second surface so as to form a cathode battery lead-out pocket into which anode and cathode battery lead-outs Ila, 11c, respectively, can be inserted so as to form a cell module 27 (See Figure 9E) incorporating an individual cell 2 and the anode and cathode battery lead-outs Ila, 11c. The anode and cathode battery lead-outs Ila, 11c slide readily in and out of their respective anode and cathode battery lead-out pockets, so that electrical contact between each cell lead-out 7a, 7c and corresponding battery lead-out Ila, 11c is maintained, even at extremities of bending.

With reference to Figure 6A to G, a cathode current collector 6c, shown in Figure 6A, is initially fabricated from, e.g. a 40 pm thick Al foil. The cathode current collector 6c is shaped so as to include an area 13 for the active material to be placed, and a “flag”-type cathode cell lead-out 7c, which is eventually used to form the cathode battery lead-out pocket into which the cathode cell battery lead-out 11c is slideably received, as will be described in more detail below.

In Figure 6B, the cathode current collector 12 has been partially covered on one side with an insulating layer 14, such as packing tape or other material, to prevent battery shorting, leaving only the cathode cell lead-out 11c for connection, and the area 13 to collect current from the active material placed on the cathode current collector 6c. The anode cell 2 can also be prepared in this way.

The insulated area is then covered, as shown in Figure 6C, with a pressure sensitive adhesive 15 to enable the anode and cathode current collectors 6a,6c to be later laminated together. An example pressure sensitive adhesive 15 is one produced by Adhesives Research Inc., (product number EL-92734). In other embodiments, a single layer may provide both adhesion and insulation. For example, an insulating layer 14 can be applied to the anode current collector 6a that has an adhesive upper surface, for example an adhesive backing layer.

A first gelled electrode stack 16a is placed on the area 13 of the current collector 6c that collects current, with the stainless steel of the stack 16 contacting the current collector 6c, as shown in Figure 6D. The active material could also be drop-cast, dispense printed, screen printed, etc.

A gel separator 17 is placed on top, as shown in Figure 6E.

A second gelled electrode stack 16b is placed on the gel separator 16, with the stainless steel layer facing upwards, as shown in Figure 6F.

The anode current collector 6a is placed onto the multilayer stack, as shown in Figure 6G. The whole device is then fed through a laminator to encapsulate the cell 2 and attain goodinterlayer contact between the separator 17 and the electrodes 16a, 16b. The process of lamination may or may not include application of heat and/or pressure when the separate layers are brought into contact or after the separate layers have been brought into contact.

Alternatively, the gelled active material stacks 16a, 16b and gel separator 17 are initially laminated together between two sheets of PET. The AM-separator-AM sandwich is then placed on the cathode current collector 6c, the anode current collector 6a is aligned on top, and the cell 2 is sealed by lamination.

Prior to assembly of a polymer battery 1 using a plurality of cells 2 described above with reference to Figures 6A to 6G, it is first necessary to fabricate the anode and cathode battery lead-outs Ila,11c and connect them to each of the cells 2. Fabrication of the lead-outs, according to one embodiment, is described with reference to Figures 7A to 7C.

With reference to Figure 7A, 40 pm thick Al foil is initially cut into 9 x 1.5 cm strips 18.

A small pinch of stainless steel wool 19, gently rolled into a sausage shape, and placed approximately 2.5 cm from the end of the Al strip 18, as shown in Figure 7B. By way of example, the stainless steel wool used was grade 0000 from Decorating Direct.

Once the stainless steel wool 19 is in place, as shown in Figure 7B, the end of the Al strip 18 is folded over along fold line F, so that the strip 18 forms a double layer with the stainless steel wool 19 contained within the fold F. Some loose stainless steel fibres 19a remain projecting out from the folded area, as can be seen in Figure 7C. Figure 7C shows a completed anode or cathode battery lead-out 1 la,l 1c. The projecting fibres improve electrical contact between the battery lead-out 1 la,l 1c and the cell lead-out 7a,7c.

Although reference is made to the placement of stainless steel wool in the fold, it will be appreciated that any resiliently deformable material may also be used, such as a piece of foam material. A resilently deformable material will bias the folded part of the battery lead-out 1 la,l 1c into electrical contact with the cell lead-out 7a,7c.

In other embodiments, multiple folds may be made in the battery cell lead-out 11 a, 11c. Alternatively, the battery cell lead-out 11 a, 11c may not be folded at all. For example, the end of the battery lead-out 1 la,l 1c may simply be treated, roughened or stamped so as to improve its electrical contact with the cell lead-out 7 a,7c. Alternatively, a conductive material, such as steel wool, may be placed in the pocket together with the battery lead-out Ila,11c without folding the battery lead-out 1 la,l 1c.

In a modified embodiment, illustrated with reference to Figures 8A to 8F, the battery cell lead outs 11 a, 11c may be reinforced with PET or any other thin, flexible material that prevents crumpling of the aluminium foil. PET, or other suitable material, is used to reinforce the aluminium battery lead-outs Ila, 11c, so when the battery 1 is bent, lateral displacement of the cell 2 is favoured over deformation of the lead-out Ila, 11c, while retaining lead-out flexibility. With reference to Figure 8B, adhesive 20 is initially applied to one surface of the Al foil and a strip 21 of 125 gm thick PET, cut to 6.5 x 1.5 cm, is stuck onto the Al foil surface 20, as shown in Figure 8C, to leave a ~ 2.5 cm strip of foil 18a at the end of the PET strip.

Next, the Al foil 18 is folded lengthways over the PET strip 21, as shown in Figure 8D.

As in the embodiment of Figures 7A to 7C, a small pinch of stainless steel wool 19 (grade 0000) is gently rolled into a sausage shape and placed approximately 2.5cm from the end of the Al strip 18 not containing PET, as shown in Figure 8E, and the end of the Al strip 18a is folded over to contain the steel wool 19 in the fold F and so that some loose stainless steel fibres 19a project out from the folded area, as shown in Figure 8F.

Assembly of a cell module 22 (see Figure 9E), using the cells 2 as fabricated above with reference to Figures 6A to 6G, together with the anode and cathode battery cell lead-outs Ila, 11c, as fabricated with reference to Figures 7A to 7C or 8A to 8E, will now be described with reference to Figures 9A to 9F.

With reference to Figure 9A, a cell 2, as assembled in Figures 6A to 6G, is vacuum sealed in a thermally sealing vacuum pouch 8, such that the cell lead-outs 7a,7c extend out from the pouch (only cell lead-out 7a being visible in Figures 9A to 9F). By way of example, the pouches 8 can be formed used vacuum bags, having dimensions 127 x 76 mm, obtained from RS Components (product number 182-8792).

The anode and cathode cell lead-outs 7a,7c are folded over the vacuum pouch 8 in opposite directions, so the anode cell lead-out 7a lies on one external surface 8a of the vacuum pouch 8, and the cathode cell lead-out 7c lies on the opposite external surface (not shown) of the vacuum pouch 8, as shown in Figure 9C.

Using, for example, packing tape 25 or other appropriate material, each of the cell lead-outs 7a,7c are secured to the vacuum pouch 8 on three sides to a form battery lead-out pocket on either side of the pouch 8, as shown in Figure 9D. The packing tape 25 extends over the cell lead-out 7a and sticks to the surface of the pouch 8a. The tape 25 is attached over the cell lead-outs 7a,7c so that one edge of the cell lead-out 7a,7c is unattached and so forms an opening 26 into the pocket between the cell lead-out 7a,7c and the pouch 8. The anode cell lead-out 7a and the cathode cell lead-out 7c of each pouch 8 are attached to the respective opposing surfaces 8a, 8b of the pouch 8 so that the openings 26 face in laterally opposite directions. The packing tape 25 additionally acts as an insulating layer to prevent shorts when the cells 2 are stacked. In particular, the insulating layer provided by the pouch 8 avoids a short circuit between the two current collectors arising from lamination of the current collector.

Next, an anode battery lead-out Ila, fabricated as described with reference to Figures 7A to 7C, or 8A to 8E, is inserted into the anode lead-out pocket of each cell 2, as shown in Figure 9E. Similarly, a cathode battery lead-out 11c, fabricated with reference to Figures 7A to 7C, or 8A to 8E, is inserted into the cathode lead-out pocket of each cell 2, so that the folded end of each of the battery lead-outs Ila,11c, containing the stainless steel wool 19, is received within a pocket. Cell 2, together with anode and cathode battery lead-outs Ila, 11c, forms a cell module 27.

The completed cell module 27, as shown in Figure 9E, are stacked on top of one another. If the cells 2 are to be connected in parallel, stacking is as shown in Figure 9F, such that the anode battery lead-out pocket of one cell 2 faces the anode battery lead-out pocket of an adjacent cell 2, and the cathode lead-out pocket of one cell 2 faces the cathode lead-out pocket of an adjacent cell 2. By stacking the cells in this way, all the cathode battery leadouts 11c extend out in one lateral direction; and all the anode battery lead-outs Ila extend out in a laterally opposite direction.

Once stacked, all the anode battery lead-outs Ila may be connected by folding the ends together. Similarly, all the cathode battery lead-outs 11c may be connected by folding their ends together, These connections are schematically shown in Figure 9F.

Final assembly of the battery shown in 9F, to encapsulate it in a flexible external package 9, will now be described with reference to Figures 10A to 10E.

Firstly, and with reference to Figure 10A, an adhesive bandage 9 is cut into two -15 cm length sections 9a,9b. By way of example, suitable adhesive elastic bandages are available from Physique (Tiger Club EAB strapping 7.5 cm x 4.5 m, part number 5924). However, other flexible or elastic materials may be employed.

Next, low-friction, e.g.Teflon, tape 10 is stuck to the adhesive side of each of the bandage sections 9a, 9b, leaving a 1 cm border along the long edges of each bandage section 9a,9b, and a 2.5 cm border along the short edges of each bandage section, as shown in Figure 10B and 10C. By way of example, suitable tape (50mm x 10m PTFE (Teflon)) is available from Fisher Scientific (part number SEL-530-010P).

With reference to Figure IOC, two holes 28 are cut at opposite ends into one of the bandage sections 9b, in an area not covered by the Teflon tape 10. However, in other embodiments, the battery lead-outs 1 la,l 1c may simply extend out of the external packaging.

Next, the Teflon-coated bandage section 9b of Figure 10C is placed with the Teflon side facing up and the battery lead-outs Ila,11c of the stack assembled as described with reference to Figures 9A to 9F, are aligned over the holes 28 and stuck to the adhesive on section 9b.

The other Teflon-coated bandage section 9a, illustrated in Figure 10B, is then placed on top of the battery stack, with the Teflon coated side facing the battery 1 and the edges of the top bandage section 9a are aligned with the corresponding edges of the bottom bandage section 9b, as shown in Figure 10D.

Finally, the adhesive edges of each bandage section 9a, 9b are pressed together to seal and complete the assembly of the battery 1, as shown in Figure 10E.

A possible method of fabricating the battery shown in Figure 3 will now be described, with reference to Figures 11A to 11G.

External packaging 9 was formed by cutting two layers 9a, 9b of Acrylonitrile butadiene (AB) rubber, one of which is shown in Figure 11A.

A strip of, for example, Parafilm tape 30 (cut to approx. 5cm x 9cm and 3cm x 9cm), were placed on top of each of the AB layers 9a, 9b, as shown in Figure 11B. The stack was then heated to 120°C to adhere the Parafilm tape 30 to the AB rubber layers 9a,9b. Rather than Parafilm tape, any thermoplastic that shows good adhesion to both the low friction surface and the battery external packaging may be used.

Teflon tape 31 (cut to 5cm x 6.5cm) was placed on top of the Parafilm layer 30 and again the stack was heated to 120°C to adhere the Teflon tape 31 to the Parafilm layer 30, before allowing the laminate to cool. Instead of Teflon, any electrically insulating surface with a low-friction coefficient may be provided.

An electrochemical cell 2, assembled as described according to any of the embodiments referred to above, is placed on the bottom encapsulation layer 9b, with the Teflon tape 31 contacting the cell 2. Each cell 2 is stacked on top of the other, with the lead-outs 7a,7c all facing in the same direction, as shown in Figure 1 ID.

Holes 28 are cut into the top encapsulation layer 9a. The lead-outs 7a,7c of the stacked cells 2 are threaded through the holes 28 in the layer 9a, with the Teflon surface 31 of the top encapsulation layer 9a contacting the stacked cells 2, as shown in Figure HE. The stacked anode cell lead-outs 7a can be connected together by folding their ends, and the stacked cathode cell lead-outs 7c are similarly connected, as shown in Figure HF. It will be appreciated that the cell-lead outs need not be connected by folding and that any means of connection may be employed. For example, the battery lead-outs may be electrically connected by stapling, welding or other joining methods.

Finally, the layers 9a, 9b are brought together and sealed by heating around the edges to 120 °C.

An example battery based on F8BT anode /F8TFB cathode polymer electrodes, as shown in Figures 4 and 5, incorporating two cells fabricated as shown in Figure 6, provided with battery cell lead outs fabricated as described with reference to Figure 7A to 7C or 8A to 8E, and encapsulated with reference to Figure 10, was tested in both straight and bent configurations. Using only a single layer of 40pm aluminium foil for the battery lead-outs 11 a,He gave poor electrical connection between cells 2, evident by only intermittent battery charging (data not shown). However, it was found that an electrical connection between battery lead-out 7a,7c and cell lead-out 1 la,l 1c was maintained, whilst retaining the ability of the battery lead-out Ila, 11c to slide within the cell lead-out pocket, by providing a small ball of fine grade stainless steel wool 19 placed between a folded strip of aluminium foil 18 forming the battery lead-outs Ila,11c, as described above with reference to Figures 7A to 7C or 8A to 8E. It was found that the stainless steel wool fibres 19 project out of the folded battery lead-out Ila, 11c and maintained contact with the cell lead-out 7a,7c. Furthermore, folding the aluminium strip 18 around the bulk of the stainless steel wool 19 provided a smooth, non-abrasive surface for sliding.

Using the stainless steel wool/aluminium foil battery lead-outs Ila,11c, a battery Qmax= _2

0.23 mAh cm’ was obtained with the battery 1 unbent, showing that both cells 2 were charging and discharging. The battery 1 was charged/discharged in this conformation for 35 cycles, before being bent to a 2.75cm radius and tested for a further 100 cycles. The battery 1 in both straight and bent conformations gave steady discharge curves, as shown in Figures 12A and 12B, respectively. Good electrical contact between cell lead-outs 7a,7c and battery lead-outs Ila, 11c is therefore demonstrated. Furthermore, a comparison between two consecutive charging/discharging cycles, where the battery 1 is unbent for the first cycle, and bent for the second, show comparable midpoint voltages and charge capacities (Table 1), which demonstrates that battery performance is not negatively impacted by flexing.

Battery i conformation Strnivlif	i Cycle number	Midpoint Voltage /V '.'ΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛ 2 04	Charge i Capacity/mAh i cm'² i	Charging Internal Resistance /Ω 1 ^ΧΧ'.'ΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛ.', 217
\| Bent (2.75 cm	ί 36	2.08	0.19	15.0 i
radius)

Table 1: Comparison of battery performance when in straight and bent configurations.

Another example battery 1, based on Schiff Base Polymer 1 anode / Polytriphenylamine 1 cathode polymer electrodes, was also tested. This battery 1 differed from the previous example in that the battery contains 3 stacked cells connected in parallel, rather than two, in that the battery uses single electrode layers containing Schiff Base Polymer 1 and Polytriphenylamine 1 polymers as anode and cathode active materials, respectively and, in that PET was used to reinforce the aluminium battery lead-outs Ila,11c. By reinforcing the battery lead-outs 11 a, 11c, lateral displacement of the cell 2 is favoured over deformation of the lead out 1 la,l 1c, while retaining lead-out flexibility when the battery 1 is bent.

Before assembly into a sliding battery structure, each individual cell 2 was tested for 5 cycles; the measured charge capacity for each cell at cycle 5 is summarised in Table 2.

Cell #	Charge Capacity at cycle 5 i
	/mAh cm'²
Ϊ	().278
2	0.203 ί
3	0.343

Table 2 Summary of individual cell charge capacities in the final cycle of testing before assembly into a battery.

The battery 1 was assembled and tested for 50 charging/discharging cycles in the straight conformation. As shown by the graph of Figure 13 A, the charge capacity of the 3 cell battery _2 on the first cycle (0.83 mAh cm’ ) corresponded to the sum of the charge capacities of each of the individual cells (0.278+0.203+0.343 = 0.824 mAh cm’²) showing good electrical connection between the three cells 2.

After completion of the 50 charging/discharging cycles, the battery 1 was bent to a 2.75cm bending radius and charged/discharged for a further 50 cycles, and the results are shown by the graph of Figure 13B. Figure 14A also shows that the battery midpoint voltage was unaffected by the change in battery conformation. An initial drop was observed in charge capacity on bending; this was likely due to a ~58h pause in battery testing, as after 10 further charge/discharge cycles the charge capacity was approximately that had the battery 1 been left to continuously cycle in the straight conformation, as shown by Figure 14B.

The ability of the 3-stack battery 1 to be bent to a 2.75cm bending radius despite its measured thickness of 4.7mm highlights how a sliding cell design allows a thick battery 1 to retain a high degree of flexibility.

The anode may comprise at least one electrochemically active polymer layer which is capable of undergoing reversible n-doping (an “n-type” polymer). The cathode may comprise at least one electrochemically active polymer layer which is capable of undergoing reversible pdoping (a “p-type” polymer).

Each cell 2 may contain three electrode layers. However it will be understood that each electrode may contain more or fewer electrode layers and the number of anode layers may be the same as or different from the number of cathode layers. The number of electrode layers may be selected according to, for example, a desired cell capacity. Preferably, the number of electrode layers is in the range of 1-15, optionally 1-10 or 1-6.

The battery 1 described herein may be capable of bending to give a circular arc of at least 10°, optionally at least 20° or 40°.

Figure 15A to 15E shows a sequence of steps involved in the formation of an individual cell 2 according to another embodiment. A plurality of these cells 2 may be incorporated into a flexible battery 1 according to an embodiment of the invention.

In the embodiment of Figures 15A to 15E, the current collectors 6a,6c also act as the battery encapsulation, and an additional vacuum pouch is not used. The current collectors 6a,6c can be made of a metal foil, or a metal-polymer laminate e.g. Al/PET. Initially, the cell 2 is assembled as described with reference to Figures 6A to 6G, as shown by Figures 15A and 15B. However, rather than encapsulating the cell 2 with the cell lead-outs 7a, 7c protruding from the encapsulation, the flag-shaped cell-lead outs 7a, 7c are folded over such that an electrically conductive surface is facing outwards on both sides of the cell 2, as shown in Figure 15C. Next, an insulating border 30a 30c is stuck to both sides of the electrochemical cell 2, as shown in Figure 15D, to prevent accidental shorts occurring when the cells 2 are stacked. The insulating border 30a, 30c has a window 31 to expose the folded-over cell leadout surface 7a, 7c, resulting in an electrochemical cell 2 with an anode surface cell lead-out 7a on one side of the cell 2, and a cathode surface cell lead-out 7c on the other side. The cell surface lead-outs 7a,7c are depressed or recessed beneath the insulating borders 30a, 30c, so for good electrical contact to be assured, the insulating border 30a, 30c needs to be very thin, and the battery lead-outs (not shown) need to be designed to project through the window 31 in the insulating border 30a, 30c.

When the cells 2 are stacked, the insulating borders 30a, 30c of adjacent cells 2 lie in contact and the cells 2 can move or displace relative to each other when the battery 1 is flexed. The insulating borders 30a,30c may be formed from, or coated with, a material having a low coefficient of friction to enhance their ability to move relative to each other.

Figure 16A to 16G shows a sequence of steps involved in the formation of an individual cell 2 according to yet another embodiment. A plurality of these cells 2 may be incorporated into a flexible battery 1 according to an embodiment of the invention and as shown in Figure 16C.

In the embodiment of Figures 15A to 15E, the insulating border 30a, 30c is placed on top of the anode and cathode lead-out surfaces 7a, 7c. Potentially, this could hinder the electrical contact of the cell lead-out surface 7 a,7c with the battery lead-out. In the embodiment of Figure 16A to 16G, an insulating border 32, having an aperture 33 is placed between the cathode and anode. As shown in Figure 16A and 16B, an insulating border 32 is first placed on the anode current collector 6a and heated to attach them together, as shown in Figure 16C. Next, active material is 16a is placed on the current collector 6a, as shown in Figure 16D. A separator 17 is then placed over the active material 16a, as shown in Figure 16E, and the cathode current collector 6c, together with active material 16a placed upon it, is placed on top of the separator 17, as shown in Figure 16F, to form the cell 2, as shown in Figure 16G. By forming the cell 2 in this way, accidental electrical shorts occurring as the cells 2 are stacked in the battery are prevented, a bank for active material deposition is provided, a gas and water-tight seal is obtained to secure the anode and cathode current collectors to one another which removes the need for a vacuum pouch, and an insulating spacer is provided to prevent electrical contact of anode and cathode within the cell 2.

As the cell lead-out surfaces 7a,7c sit on top of the insulating border 32 rather than being recessed beneath it, contact with the battery lead-outs 1 la, 11c, is unobstructed.

With reference to Figure 17, which shows a schematic view of a flexible battery 1 assembled from four of the cells 2 assembled according to Figures 16A to 16G, the battery lead-outs Ila, 11c slide past the conductive surface lead-outs 7a, 7c, to make electrical contact, rather than into a battery lead-out pocket, as previously described above with reference to Figures 6 to 9.

A battery 1 as described herein may be used as a power source for any device, preferably for a portable device such as a phone, tablet or laptop, or a wearable device. A battery as described herein may be provided on a card, for example a debit, credit, prepayment or business card comprising an electrical device including, without limitation, a display, a speaker, a transmitter or a receiver.

Although the present invention has been described in terms of specific exemplary embodiments, it will be appreciated that various modifications, alterations and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims.

Claims

1. A flexible battery comprising a stack of electrochemical cells, each cell being movable relative to an adjacent cell when the battery is bent.

2. A flexible battery according to claim 1, comprising an insulating layer between each cell.

3. A flexible battery according to claim 2, wherein the insulating layer is formed from a material to enable adjacent cells to move relative to each other.

4. A flexible battery according to any preceding claim, comprising a flexible external package, said stack of electrochemical cells being received in said flexible external package.

5. A flexible battery according to claim 4, wherein the flexible external package is formed from an elastic material.

6. A flexible battery according to claim 4 or 5, wherein the flexible external package and the outermost cells of the stack are movable relative to each other.

7. A flexible battery according to claim 6, wherein an inner surface of the flexible external package is covered with a material that allows the outermost cells and the flexible external package to move relative to each other.

8. A flexible battery according to any of claims 2 to 7, wherein each electrochemical cell comprises an anode, a cathode; a separator between the anode and the cathode; an anode current collector; and a cathode current collector.

9. A flexible battery according to claim 8, wherein each cell comprises a pouch encapsulating the anode, the cathode, the separator between the anode and the cathode, the anode current collector and the cathode current collector, and the insulating layer is formed by the pouch.

10. A flexible battery according to claim 9, wherein an anode cell lead-out extends from the anode current collector out of the pouch and, a cathode cell lead-out extends from the cathode current collector out of the pouch.

11. A flexible battery according to claim 10, wherein the anode cell-lead out is integral with the anode current collector, and the cathode cell lead-out is integral with the cathode current collector.

12. A flexible battery according to claim 9 or 10, wherein the anode cell lead-outs of the electrochemical cells are directly connected to each other, and the cathode cell leadouts of the electrochemical cells are directly connected to each other.

13. A flexible battery according to claim 9 or 10, comprising an anode battery lead-out extending from, and in electrical connection with, each anode cell lead-out, and a cathode battery lead-out extending from, and in electrical connection with, each cathode cell lead-out, so that each cell, together with its anode and cathode battery lead-outs, forms a cell module.

14. A flexible battery according to claim 13, wherein the anode cell lead-out and the anode battery lead-out of each cell module are slideable relative to each other, and wherein the cathode cell lead-out and the cathode battery lead-out of each cell module are slideable relative to each other.

15. A flexible battery according to claim 14, wherein each cell module comprises an anode battery lead-out pocket to slideably receive the anode battery lead-out, and a cathode battery lead-out pocket to slideably receive the cathode battery lead-out.

16. A flexible battery according to claim 15, wherein the anode battery lead-out pocket is formed between the anode cell lead-out and a first external surface of the pouch, and the cathode battery lead-out pocket is formed between the cathode cell lead-out and a second external surface of the pouch opposite to said first external surface.

17. A flexible battery according to claim 16, wherein the anode cell lead-out is attached to the first external surface, and the cathode cell lead-out is attached to the second external surface.

18. A flexible battery according to claim 17, comprising an insulating layer extending over said anode cell lead-out that attaches said anode cell lead-out to said first external surface such that an opening is formed along an edge of the anode cell lead out to provide access to the anode battery lead-out pocket, and an insulating layer extending over said cathode cell lead-out that attaches said cathode cell lead-out to said second external surface such that an opening is formed along an edge of the cathode cell lead-out to provide access to the cathode battery lead-out pocket.

19. A flexible battery according to any of claims 15 to 18, wherein an end of each of the anode and cathode battery lead-outs is received in respective anode and cathode battery lead-out pockets to extend therefrom.

20. A flexible battery according to claim 19, wherein said end of each of the anode and cathode battery lead-outs is folded back on itself to form a double layer within the anode and cathode lead-out pockets, respectively.

21. A flexible battery according to claim 20, wherein a resiliently deformable material is received in the fold between said double layer of respective anode and cathode battery lead-outs.

22. A flexible battery according to claim 21, wherein said resiliently deformable material is a conductive wool.

23. A flexible battery according to claim 22, wherein said resiliently deformable conductive wool is received in the fold between said double layer of respective anode and cathode battery lead-outs so as to protrude out of said fold.

24. A flexible battery according to any of claims 15 to 23, wherein said anode and cathode battery lead-out pockets of each cell module are each configured so that the anode battery lead-out extends laterally from said anode battery lead-out pocket in one direction, and the cathode battery lead-out extends laterally from said cathode battery lead-out pocket in the opposite direction.

25. A flexible battery according to claim 24, wherein the cell modules are arranged such that the anode battery lead-out pocket of one cell faces the anode battery lead out pocket of an adjacent cell such that the anode battery lead-outs of all the cells extend in the same direction, and such that the cathode battery lead-out pocket of one cell faces the cathode battery lead-out pocket of an adjacent cell such that the cathode battery lead-outs of all the cells extend in the same direction.

26. A flexible battery according to claim 25, wherein the direction in which the anode battery lead-outs extend is laterally opposite to the direction in which the cathode battery lead-outs extend.

27. A flexible battery according to claim 26, wherein all the anode battery lead-outs are electrically connected to each other at their free ends remote from said anode battery lead-out pockets, and all the cathode battery lead-outs are electrically connected to each other at their free ends remote from said cathode battery lead-out pockets.

28. An electrochemical cell for a flexible battery comprising a pouch having first and second opposing external surfaces, the pouch containing an anode, a cathode; a separator between the anode and the cathode; an anode current collector; and a cathode current collector, wherein an anode cell lead-out extends from the pouch and is attached to said first external surface to form an anode battery lead-out pocket, and a cathode cell lead-out extends from the pouch and is attached to said second external surface to form a cathode battery lead-out pocket.

29. A cell according to claim 28, wherein the anode cell lead-out is integrally formed with the anode current collector, and the cathode cell lead-out is integrally formed with the cathode current collector.

30. A cell module comprising the cell according to claim 28 or 29, and an anode battery lead-out slideably received in the anode battery lead-out pocket, and a cathode battery lead-out slideably received in the cathode battery lead-out pocket.

31. A cell module according to claim 30, wherein an end of each of the anode and cathode battery lead-outs received in respective anode and cathode battery lead-out pockets is folded back on itself to form a double layer.

32. A cell module according to claim 31, wherein a resiliently deformable material is received in the fold between said double layer.

33. A method of forming a flexible battery comprising a stack of electrically connected electrochemical cells, the method comprising stacking the cells such that each cell can move relative to an adjacent cell when the battery is bent.

34. A method according to claim 33, wherein each cell is separated from an adjacent cell by an insulating layer that enables the cells to move relative to each other.

35. A method according to claim 34, wherein the method includes inserting the plurality of electrochemical cells into a flexible external package.

36. A method of forming an electrochemical cell for a flexible battery comprising inserting an anode, a cathode; a separator between the anode and the cathode; an anode current collector; and a cathode current collector, into a pouch having first and second opposing external surfaces, and such that anode and cathode cell lead-outs extend from the pouch, attaching said anode cell lead-out to the first external surface to form an anode battery lead-out pocket, and attaching said cathode cell lead-out to the second external surface to form a cathode battery lead-out pocket.

37. A method of forming a cell module according to any of claims 30 to 32, comprising inserting an anode cell battery lead-out into the anode battery lead-out pocket of a cell according to claim 28 or 29, and inserting a cathode cell battery lead-out into the cathode battery lead-out pocket of the cell according to claim 28 or 29.

38. A method of forming a cell module according to claim 37, including folding an end of each of the anode and cathode cell battery lead-outs prior to insertion of said ends into respective anode and cathode battery lead-out pockets.

39. A method according to claim 38, including placing a resiliently deformable material into the fold of the anode and cathode battery cell lead-outs prior to insertion of the anode and cathode battery cell lead-outs into respective anode and cathode battery lead-out pockets.