GB2572346A

GB2572346A - Electrode, battery and method

Info

Publication number: GB2572346A
Application number: GB1804861.1A
Authority: GB
Inventors: Kugler Thomas; Claire O'Sullivan Melanie; Giguere Jean-Benoit
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2018-03-27
Filing date: 2018-03-27
Publication date: 2019-10-02
Also published as: GB201804861D0

Abstract

A freestanding anode or cathode film 101, 105 comprises a conductive mesh 111 and, respectively, an n-type or p-type electrochemically active polymer wherein at least some of the n-type or p-type electrochemically active polymer is disposed in pores of the conductive mesh. The anode or cathode film 101,105 may be used as an electrode layer of a polymer battery electrode. Such electrodes may contain further electrode layers 101', 105' which do not contain a conductive mesh. The anode and/or cathode films 101, 105 may also include a conductive carbon material such as carbon black, carbon fibre, graphite or carbon nanotubes. The film(s) may also include an electrolyte, especially an ionic liquid electrolyte such as 1-butyl-1-methylpyrrolidinium bis(trifluoromethane)sulfonimide. A battery comprising an anode current collector 107, a cathode current collector 109, an anode layer 101 with a mesh 111 and an n-type polymer, a cathode layer 105 with a mesh 111 and a p-type polymer, and a separator 103 between the anode and cathode is also disclosed. The battery may be vacuum sealed within a pouch. A method of forming the battery is also disclosed.

Description

The present invention relates to polymer battery cells, electrodes for use therein and methods of forming the same.

Background of the Invention

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.

US 2012/0276434 discloses a flexible battery in which anode-type electroactive material is embedded in a mesh material and a cathode-type electroactive material is embedded in a mesh material.

WO 2016/140738 discloses a metal mesh electrode comprising a metal mesh, a thin layer of active electrode material deposited on the mesh and a thin layer of electrolyte deposited on the electrode material layer.

US 4717634 discloses a cell containing polyaniline as the positive active material of the cell anode and lithium or lithium alloy as the positive active material of the cell cathode. The polyaniline is formed by electrolytic polymerisation of aniline on a mesh substrate.

It is an object of the invention to provide a simple method for forming electrodes of a polymer battery, and a polymer battery containing said electrodes.

Summary of the Invention

The present inventors have found that a battery having low resistance may be formed by using an electrode containing a conductive mesh in contact with a current collector.

In a first aspect the invention provides a freestanding anode or cathode film comprising a conductive mesh and, respectively, an n-type or p-type electrochemically active polymer wherein at least some of the n-type or p-type electrochemically active polymer is disposed in pores of the conductive mesh.

In a second aspect the invention provides a method of forming a freestanding composite electrode film according to the first aspect, the method comprising the step of depositing a formulation comprising the n-type or p-type electrochemically active polymer dissolved or dispersed in one or more solvents onto a surface of the conductive mesh supported on a filmforming substrate; evaporating the solvent or solvents to form a film; and separating the film from the film-forming substrate.

In a third aspect the invention provides a battery comprising an anode, a cathode, a separator between the anode and the cathode, an anode current collector and a cathode current collector, wherein the anode comprises a first anode layer comprising a n-type polymer and a conductive mesh in direct contact with the anode current collector or the cathode comprises a first cathode layer comprising an p-type polymer and a conductive mesh in direct contact with the cathode current collector.

In a fourth aspect the invention provides method of forming a battery according to the third aspect, wherein the first anode layer or the first cathode layer is formed by lamination of, respectively, a freestanding anode or cathode layer according to the first aspect.

In a fifth aspect, the invention provides a battery obtainable by method according to the fourth aspect. By “freestanding electrode film” as used herein is meant an electrode layer which is not attached to or supported by another structure.

By “lamination” as used herein is meant bringing two or more layered structures into contact with one another to form a laminate structure, wherein each layered structure comprises at least one layer. 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. Two layers laminated together as described herein may or may not adhere to one another following lamination.

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 polymer battery cell according to an embodiment containing only one anode and only one cathode layer;

Figure 2 illustrates a polymer battery cell according to an embodiment containing a plurality of anode layers and a plurality of cathode layers;

Figure 3 illustrates a flexible polymer battery according to an embodiment;

Figure 4 illustrates a method of forming a flexible polymer battery according to an embodiment;

Figure 5 is a plot of discharge curves (voltage vs charge capacity) across 250 chargedischarge cycles for a battery according to an embodiment;

Figure 6 is a plot of discharge curves (voltage vs charge capacity) for a comparative battery;

Figure 7A is a plot of discharge curves (voltage vs charge capacity) for 4 charge-discharge cycles for a battery according to an embodiment; and

Figure 7B is a plot of discharge curves (voltage vs charge capacity) for a further 2 chargedischarge cycles for the battery of Figure 7A.

Detailed Description of the Invention

Figure 1, which is not drawn to any scale, illustrates a battery cell 100 according to an embodiment comprising an anode comprising an anode layer 101, a cathode comprising a cathode layer 105, a separator 103 between the anode and the cathode, an anode current collector 107 in contact with the anode and a cathode current collector 109 in contact with the cathode.

The anode comprises at least one electrochemically active polymer which is capable of undergoing reversible n-doping (an “n-type” polymer), n-type polymers as described herein preferably have a EUMO level measured by square wave voltammetry of between -4.5 and -

1.5 eV, more preferably between -3.5 and -2.0 eV

The cathode comprises at least one electrochemically active polymer which is capable of undergoing reversible p-doping (a “p-type” polymer), p-type polymers as described herein preferably have a HOMO level measured by square wave voltammetry of between -4.5 and -

6.5 eV, more preferably between -4.8 and -6 eV.

The anode comprises a first anode layer 101 which comprises a conductive mesh 111 in direct contact with anode current collector 107. First anode layer 101 further comprises an ntype polymer. First anode layer 101 may consist of the conductive mesh and n-type polymer or may comprise one or more further materials.

The cathode comprises first cathode layer 105 which comprises a conductive mesh 111 in direct contact with cathode current collector 109, which may be the same as or different from the conductive mesh 111 in direct contact with the anode current collector. First cathode layer 105 further comprises a p-type polymer. First cathode layer 105 may consist of the conductive mesh and p-type polymer or may comprise one or more further materials.

At least part of a surface of the conductive mesh of each first electrode layer is in direct contact with the corresponding current collector.

The thickness of first electrode layer (i.e. anode layer 101 or cathode layer 105) is at least the same as the thickness of the conductive mesh lllof that layer; in the embodiment illustrated in Figure 1, the electrode layers are thicker than the conductive mesh. The n- or p-type polymer or polymers of the first electrode layer may be completely contained within the thickness of the conductive mesh or may extend beyond the thickness of the conductive mesh.

In the embodiment of Figure 1, the anode consists of first anode layer 101 and the cathode consists of first cathode layer 105.

Figure 2 illustrates a further embodiment in which each of the anode and cathode is a stack comprising, respectively, first anode layer and additional anode layers 10Γ and first cathode layer 105 and additional cathode layers 105’. The additional anode and cathode layers preferably do not comprise a conductive mesh. Each additional anode layer 101’ comprises or consists of an n-type polymer. Each additional cathode layer 105’ comprises or consists of a p-type polymer.

An anode or cathode stack containing a plurality of electrode layers may be formed to a desired electrode thickness without cracking of the electrode, as may occur during drying when an electrode is formed by deposition of a formulation onto a current collector followed by drying to remove solvent(s) of the formulation.

The component or components of each additional anode layer 10 Γ or cathode layer 105’ may be the same as first anode layer 101 or first cathode layer 105, respectively, preferably except for the conductive mesh.

Additional materials present in an anode layer 101 or 10Γ or in a cathode layer 105 or 105’ include, without limitation, conductive carbon and an electrolyte.

Figure 2 illustrates a battery with three anode layers and three cathode layers. In other embodiments, the number of anode or cathode layers may be greater or smaller. In other embodiments, the anode and cathode may have different numbers of electrode layers. The number of electrode layers may be selected according to, for example, a desired cell capacity. Preferably, the number of electrode layers of the anode and / or the cathode is in the range of 1-15, optionally 1-10 or 1-6.

Figure 2 illustrates a battery in which each of the anode and cathode consists of a first electrode layer and one or more further electrode layers. In other embodiments, an anode stack or a cathode stack may comprise one or more layers which not comprise an n-type polymer or p-type polymer, preferably one or more electrolyte layers.

An electrolyte layer is disposed between at least one pair of adjacent electrode layers in the stack, and preferably between each pair of adjacent electrode layers. The intermediate electrolyte layer preferably comprises a polymer and an electrolyte and may be a solid or gel layer. It will be appreciated that a pair of adjacent electrode layers do not directly contact one another across at least part or all of their surface areas if an intermediate electrolyte layer is provided therebetween. At least some of the surfaces of adjacent electrode pairs may be in direct contact and optionally a majority of the overlapping surfaces of adjacent electrode pairs may be in direct contact. It will therefore be appreciated that the electrolyte layer as described herein may be a discontinuous layer and / or a layer containing one or more apertures.

An electrode containing adjacent electrode layers which are in direct contact may have enhanced electrical conductivity (as distinct from ionic conductivity) as compared to an electrode in which adjacent electrode layers which are not in direct contact. The extent of direct contact between adjacent electrode layers may be determined, at least in part, by the average thickness of any electrolyte layer between the adjacent electrode layers.

The anode and cathode illustrated in Figures 1 and 2 each contain a conductive mesh 111. In other embodiments, only one of the anode and cathode contains a conductive mesh.

Each electrode layer described herein, including each first electrode layer and each additional electrode layer, may be formed from a freestanding electrode film.

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

An exemplary flexible battery is illustrated in Figure 3, which is not drawn to any scale, in which the battery has flexible anode and cathode current collectors 107, 109 for example metal foil current collectors. The separator 103 has a perimeter dimension (length or width) which is at least the same as that of the current collectors, preferably greater than that of the current collectors. Any parts of the two current collectors which fall outside the separator perimeter are arranged such that they do not contact one another, for example during flexing or lamination of the device.

The flexible battery may be sealed in flexible packaging 111. Apertures 115 in the flexible packaging expose the anode and cathode current collectors for connection to conductive leadouts 113, suitably flexible lead-outs, for example metal tape such as copper tape or aluminium tape or a printed metal ink, for example printed silver ink.

The battery may be sealed by lamination between two plastic sheets. Preferably, heat and pressure are applied during lamination to fuse the two plastic sheets. Lamination sealing may be carried out using a lamination machine comprising two rollers through which a flexible structure may be passed. Preferably, the rollers are heated when in use. Alternatively or additionally, the flexible packaging is a vacuum sealed enclosure in which lead-outs 113 extend beyond the perimeter of the flexible packaging to allow connection of the battery.

Anode and cathode lead-outs 113 illustrated in Figure 3 are on opposite ends of the same side of the battery, however it will be appreciated that lead-outs as described anywhere herein may have other arrangements, for example on opposing sides of the battery.

The flexible anode and cathode current collectors of a flexible battery may be laminated together so as to encapsulate the device. An insulating layer may be provided on a surface of at least one of the flexible current collectors outside an area occupied by the anode, cathode and separator to avoid a short circuit between the two current collectors arising from lamination of the current collector.

Figure 4, which is not drawn to any scale, illustrates a process of forming a battery encapsulated by its current collectors.

A surface of anode current collector 107 of a metal foil is covered by an insulating layer 115 of an insulating material, for example an adhesive insulating tape to define an exposed current collector area Al surrounded by the insulating material. The whole of the surface of the metal foil may be covered except for battery area Al and a lead-out area A2. A lead out area A2 may be provided on the same surface of metal foil 107 as battery area Al if, for example, the opposing surface of the metal foil has an insulating backing such as PET-backed aluminium foil. In other embodiments, both surfaces of the current collector 107 are conductive and a connection may be made to the surface of the metal foil opposite battery area Al in which case area A2 on the same side of the current collector as area Al may or may not be covered.

An adhesive layer 117, for example a layer of pressure-sensitive adhesive, is provided on the insulating layer. In other embodiments, a single layer provides both adhesion and insulation; for example the insulating layer 115 as applied to the anode current collector 107 has an adhesive upper surface, for example an adhesive backing layer. The anode, comprising or consisting of anode layer 101, is placed within the battery area Al such that the conductive mesh contacts the metal foil. A separator 103 is provided over the anode. The separator overlaps battery area Al, and preferably extends beyond the perimeter of battery area Al. A cathode comprising or consisting of cathode layer 105 (not shown in Figure 4) is disposed over the separator so as to at least partially or completely overlap with the underlying anode and such that the conductive mesh of cathode layer 105 is uppermost, and a metal foil cathode current collector 109 is applied over and around battery area Al and adhered to adhesive layer 117. The cathode current collector has a lead out area A3.

In other embodiments, two or all three of the anode, cathode and separator may be combined and then applied to the anode current collector 107. Cathode current collector 109 may or may not have an insulating layer and / or adhesive layer defining an exposed battery area Al, which may be the same as or different from battery area Al, and / or a lead-out area A3.

The completed battery is sealed, preferably vacuum sealed in a vacuum bag 119. Adhesive tabs (not shown) may be applied to both sides of each lead out in the region where the lead outs exit the sealing structure. Additionally or alternatively, the battery may be sealed by lamination sealing as described with reference to Figure 3.

In other embodiments, a flexible battery may be formed as described with respect to Figure 3 except that the isolating layer defining aperture Al is formed on cathode current collector 109 rather than anode current collector 107.

In other embodiments, a flexible battery may be formed as described with respect to Figure 4 except that the insulating layer 115 is supported on a surface of one of the anode and cathode current collectors and the adhesive layer 117 surface is supported on a surface of the other of the anode and cathode current collectors.

Figure 4 describes building up a battery structure on anode current collector 107. In other embodiments, the battery is built up on cathode current collector 109.

In other embodiments, the anode, cathode and separator may be formed on a surface of a current collector which does not carry an insulating layer and the opposing current collector carries an insulating layer defining battery area Al which is aligned with the electrode it is formed over.

First electrode film formation

A mesh-containing film suitable for forming a first electrode layer as described herein may be formed by depositing a formulation comprising one or more solvents and either one or more n-type polymers or one or more p-type polymers onto the conductive mesh supported on the surface of a substrate, hereinafter described as a film-forming substrate, followed by evaporation of the solvent or solvents.

Preferably, the n-type or p-type polymer (or at least one of the n-type polymers or at least one of the p-type polymers if there is more than one of an n-type or p-type polymer in the formulation) is dissolved in the solvent or solvents. Other components of the formulation, if present, may be dissolved or dispersed in the formulation. It will therefore be understood that the solvents as described herein do not necessarily dissolve all components of the formulation.

Other components include, without limitation, one or more electrolytes and one or more forms of conductive carbon. Preferably, the formulation does not comprise any polymers other than the or each n-type or p-type polymer.

Exemplary solvents include, without limitation, cyclic ethers and aromatic solvents, preferably benzene, substituted with one or more substituents selected from Cmo alkyl; Cmo alkoxy; and halogens, optionally bromine or chlorine, such as o-dichlorobenzene; o-xylene; and anisole.

The film-forming substrate may be selected such that there is limited or no adhesion between the film-forming substrate and the formulation in order to limit or avoid cracking during the drying of the formulation. Preferably, the substrate is a glass or plastic substrate. The filmforming substrate may consist of a single material or it may comprise two or more materials, for example a first layer supporting a second layer having an outermost surface onto which the formulation is deposited. A material having high surface smoothness may be selected for use as the film-forming surface of the film-forming substrate.

The formulation may be dried at room temperature or it may be heated. The substrate may be heated before, during or after deposition of the formulation, for example by placing the substrate on a hotplate or in an oven. The heating temperature may be selected according to the boiling point of the solvent or solvents of the formulation. Optionally, heating is carried out at a temperature in the range of about 50 - 200°C, preferably about 50 - 100°C.

The formulation may be dried at atmospheric pressure or under reduced pressure.

The film formed following evaporation of the solvent or solvents is separated from the substrate to give a freestanding first (mesh-containing) electrode film.

The materials of the formulation preferably adhere to the mesh and may or may not adhere to the substrate. If adhesion occurs between the materials of the formulation and the substrate then the film may or may not detach from the substrate during drying. Accordingly, it will be understood that “separating” the first electrode film from the substrate as used herein means removal of the first electrode film from contact with the substrate wherein the first electrode film following drying may or may not be adhered to the substrate surface.

The freestanding first electrode film may be used to form the first electrode layer of a battery without any further treatment following its separation from the film-forming substrate, or it may be subjected to one or more further treatment steps before use.

The freestanding first electrode film may be subjected to a further drying treatment, optionally at a temperature in the range of about 50 - 200°C, preferably about 50 - 100°C, at atmospheric pressure or reduced pressure before being used in a battery.

The freestanding first electrode film may be treated to remove any components of the formulation which may have dried onto the bottom surface of the conductive mesh. Preferably, the conductive mesh is releasably secured to the film-forming substrate before the formulation is applied thereto, in order to prevent or limit ingress of the formulation between the substrate and the bottom surface of the conductive mesh. Alternatively or additionally, the formulation is deposited onto the mesh in an amount that does not cover the upper surface of the mesh.

Preferably, freestanding first electrode films as described herein have a thickness in the range of 50-750 microns, optionally 50-500 microns.

Freestanding first electrode films as described herein may be stored in airtight and / or watertight packaging prior to use.

Further electrode film formation

Freestanding further electrode films for forming further electrode layers may be formed, treated and / or stored as described with respect to formation, treatment and storage of the first electrode films except that the formulation for forming the further electrode films is deposited directly onto the film-forming substrate (i.e. in the absence of the conductive mesh).

The formulations for forming the first electrode film and a further electrode film used to form the electrode layers of a battery may be the same or different.

Preferably, freestanding further electrode films as described herein have a thickness in the range of 10-100 microns, optionally 25-90 microns.

Conductive mesh

The mesh is preferably a 2 dimensional mesh structure defining pores between wires of the conductive mesh. In other embodiments, the mesh is a 3-dimension mesh structure wherein a perimeter of the mesh defines a volume.

The wires of the conductive mesh preferably have a thickness in the range of about 10-200 microns, preferably 10-150 microns, most preferably 10-75 microns.

The wires of the mesh may define pores of any shape. Preferably, the pores have a size of 10-200 microns, preferably 30-100 microns. In the case of a mesh defining square pores, the pore size is the length of an edge of the pores.

The conductive mesh preferably has a porosity of 20-75 %, optionally 30-75 % wherein porosity is the percentage of the surface area of the mesh which is mesh pores. The conductive mesh may comprise or consist of any conductive material, preferably a metal or metal alloy. The metal or metals of the conductive material preferably have a work function of more than 4.0 eV, and are most preferably iron, copper or aluminium. Stainless steel mesh is particularly preferred.

Work functions of metals are as given in the CRC Handbook of Chemistry and Physics, 12114, 87^th Edition, published by CRC Press, edited by David R. Lide. If more than one value is given for a metal then the first listed value applies.

A sheet of conductive mesh may be cut to the required size for use in a first electrode layer before deposition of a formulation onto the conductive mesh to form a first electrode film, or the first electrode film may be cut to the required size.

If the first electrode film is cut to the required size it may be cut before or after it is used to form an electrode layer of a battery.

Battery formation

According to an embodiment, formation of a battery cell as described herein may include the following steps:

(i) Lamination of a first anode film and, optionally, one or more further anode films and an anode current collector.

(ii) Lamination of a first cathode film and, optionally, one or more further cathode films and a cathode current collector.

(iii) Lamination of a separator comprising an electrolyte between the anode and cathode

Steps (i), (ii) and (iii) may occur in any sequence.

One of steps (i) and (ii) may be replaced by another process for forming the anode or cathode if only one of the anode and cathode contains a conductive mesh. For example, one of steps (i) and (ii) may be replaced by a step of lamination of electrode films which do not contain a conductive mesh, or a step of depositing the components of the electrode onto a current collector followed by evaporation of the solvent or solvents of the formulation.

According to other embodiments, a first anode film and, optionally, one or more further anode films and / or a first cathode film and, optionally, one or more further cathode films may be laminated to the separator followed by lamination of the corresponding current collector(s) to the combined electrode / separator structure.

It will be understood that a freestanding electrode film as described herein ceases to be freestanding following lamination to another structure, for example a current collector, separator or another freestanding electrode film.

Where an electrode is formed by lamination of one or more freestanding electrode films to a current collector or separator, it is preferred that the electrode is formed from a plurality of freestanding electrode films, optionally 2-15 freestanding electrode films including a first electrode film, laminated together. The plurality of freestanding electrode films may be laminated sequentially onto the current collector or the separator or the plurality of freestanding electrode films may be laminated together before being laminated to the current collector or separator.

An electrode stack comprising a plurality of electrode layers formed from freestanding electrode films may be stored in airtight and / or watertight packaging before use.

An electrolyte in liquid form may be applied to one or both surfaces of freestanding electrode films before the films are laminated together. The presence of the electrolyte may enhance ionic conductivity of the electrode.

An electrode comprising one or more electrode layers formed from freestanding electrode films may consist of the one or more electrode layers or may comprise one or more layers which do not comprise an n-type or p-type polymer, preferably an electrolyte layer comprising an electrolyte, for example a solid or gel layer comprising or consisting of an electrolyte dispersed in a polymer.

Electrolytes

The electrolyte may be a dissolved salt or an ionic liquid.

The electrolyte may be a solution of a salt having an organic or metal cation, for example lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or lithium hexafluorophosphate, in an organic solvent, optionally propylene carbonate.

Ionic liquids as described herein may be ionic compounds that are liquid at below 100 °C and at 1 atm pressure. Examples include, without limitation, compounds with an ammonium-, imidazolium-, phosphonium-, pyridinium-, pyrrolidinium- or sulfonium cation. The ionic liquid may have a sulfonimide anion, for example bis(trifluoromethane)sulfonimide (TFSI) ionic liquids such as e.g. l-ethyl-3-methyl imidazolium bis(trifluoromethane)sulfonimide (EMI-TFSI), triethylmethoxyethyl phosphonium bis(trifluoromethane)sulfonimide (TEMEPTFSI), triethyl sulfonium bis(trifluoromethane)sulfonimide (TES-TFSI) or 1-butyl-lmethylpyrrolidinium bis(trifluoromethane)sulfonimide (BMP-TFSI), the latter being particularly preferable.

The freestanding anode and / or cathode films described herein may contain an electrolyte, optionally in an amount of 10-30 wt % of the freestanding electrode film.

Conductive carbon

Preferably at least one of the anode and cathode, and more preferably both of the anode and cathode, comprises one or more conductive carbon materials. Conductive carbon materials may be selected from, without limitation, one or more of the group consisting of carbon black, carbon fiber, graphite, and carbon nanotubes. . Preferably, the BET specific surface area of the conductive carbon material is in the range of 10 m /g to 3000 m /g. Preferably, conductive carbon materials as described herein have an average diameter as measured by a scanning electron microscope of 50-100 nm. Preferably, carbon black is present in electrodes described herein, either alone or with one or more other forms of conductive carbon.

Where present, a conductive carbon material may form 10-50 weight % of a freestanding electrode film.

The process of forming an electrode stack as described herein may include the step of squeezing together the layers of a stack, for example by passing the stack through a laminating machine.

If one or more electrolyte layers are present then any excess material present in the electrolyte layer or layers may be squeezed out, thereby adjusting the electrolyte layer or layers to a desired thickness and / or to bring electrode layers spaced apart by the electrolyte layer or layers as applied into direct contact with one another. Squeezing is suitably performed when the layer comprising the polymer and electrolyte is in a state which is capable of flowing, for example a paste. If the polymer of the electrolyte layer or layers of the final electrode stack is crosslinked then crosslinking is performed after any squeezing step n- and p-type polymers n-type and p-type polymers as described herein are preferably conjugated polymers. A conjugated polymer as described herein comprises adjacent repeat units which are directly linked and conjugated to one another through conjugating groups of the repeat units. A conjugating group as described herein may be a non-aromatic double bond or triple bond, an aromatic group, a heteroaromatic group or an atom having a lone pair of electrons such as a N atom. The backbone of a conjugated polymer is conjugated along at least some of its length.

Preferably, at least 25 weight %, optionally at least 30 weight % or 40 weight % of a freestanding electrode layer as described herein is made up of an electrochemically active polymer, optionally 25-90 weight %.

An n-type polymer may comprise or consist of one or more 5-20 membered monocyclic or polycyclic heteroaromatic repeat units comprising one or more N atoms, and optionally one or more arylene repeat units.

Heteroaromatic repeat units comprising one or more N atoms may comprise 0.1-99 mol % of the repeat units of the polymer, more preferably 10-75 mol %.

Heteroaromatic repeat units comprising one or more N atoms, include, without limitation, pyridine, quinoline, benzothiadiazole, benzotriazole and triazine each of which may be unsubstituted or substituted with one or more substituents, optionally one or more substituents selected from R¹ as described above.

A particularly preferred heteroaromatic repeat unit is a repeat unit of formula (IV):

(IV) wherein R⁵ in each occurrence is the same or different and is H or a substituent.

Optionally, each R⁵ is independently selected from the group consisting of:

F,

CN;

NO₂;

Ci-20 alkyl wherein one or more non-adjacent, non-terminal carbon atoms may be replaced with O, S, -Si(R⁹)2- C=O or COO wherein R⁹ in each occurrence is independently a substituent, preferably a Ci_2o hydrocarbyl group; and a group of formula -(Ar¹^ wherein Ar¹ in each occurrence is an aryl or heteroaryl group, preferably phenyl, which is unsubstituted or substituted with one or more substituents and m is at least 1, optionally 1, 2 or 3.

Substituents of Ar⁴, if present, are preferably selected from Ci_2o alkyl wherein one or more non-adjacent, non-terminal carbon atoms may be replaced with O, S, -Si(R⁹)2- C=O or COO.

A p-type polymer may comprise or consist of one or more amine repeat units, and optionally one or more arylene repeat units.

Amine repeat units of a p-type polymer suitably comprise a N atom in the polymer backbone, for example as disclosed in WO 99/54385, the contents of which are incorporated herein by reference.

Amine repeat units as described herein may have formula (V) or (VI):

(V) (VI) wherein Rn to R19 are independently selected from hydrogen, Ci-20-alkyl, Ci-20-alkyl ether, Ci_2o-carboxyl, Ci_2o-carbonyl, Ci_2o-ester, Ce-is-aryl, Cs-is-heteroaryl; n is greater than or equal to 1 and preferably 1 or 2; and Z3 is selected from a single bond, Ci_2o-alkylene, optionally substituted Ce is-arylene, or an optionally substituted Cs-is-heteroarylene group.

In preferred embodiments, R12 to R19 are independently selected from hydrogen, Ci_i2-alkyl, Ci_i2-alkyl ether, Ci_i2-carboxyl, Ci_i2-carbonyl, Ci_i2-ester, optionally substituted Ce-n-aryl, and optionally substituted Cs-n-heteroaryl groups; Z3 is selected from a single bond, an optionally substituted Ci-12-alkylene, optionally substituted Ci-12-oxyalkylene, optionally substituted Ce-n-arylene, or an optionally substituted Ce-n-heteroarylene group. Where present, substituents of a Ce-n-arylene, or a Ce-n-heteroarylene group Z3 are optionally selected from Cl-20 alkyl in which one or more non-adjacent, non-terminal C atoms may be replaced with O. In one embodiment, Z3 is an optionally substituted phenylene group, with the residue Rn being preferably an oligo- or polyether group having at least two alkoxy repeat units and being located in m- or p-position relative to the arylamino group.

A preferred amine repeat unit is 4,4’-linked triphenylamine which may be unsubstituted or substituted with one or more substituents as described above.

Amine repeat units may make up 0.1-100 mol % of the repeat units of a p-type polymer, more preferably 10-75 mol %.

Arylene repeat units of n-type or p-type polymers include, without limitation, repeat units of formulae (VII) - (IX):

(VII) (VIII)

(IX) wherein R³ in each occurrence is a substituent and R⁴, R⁶, R⁷ and R⁸ independently in each occurrence is H or a substituent.

Q

Optionally, each R is selected from the group consisting of Ci_2o alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with O, COO or CO; unsubstituted phenyl; and phenyl substituted with one or more Ci_i₂ alkyl groups wherein one or more nonadjacent, non-terminal C atoms of the alkyl groups may be replaced with O, COO or CO.

Optionally, R⁴, R⁶, R⁷ and R⁸ independently in each occurrence is H or a substituent selected from Ci-20 hydrocarbyl, optionally Ci_2o alkyl; unsubstituted phenyl; and phenyl substituted with one or more C1-12 alkyl groups.

Polymers containing aromatic or heteroaromatic repeat units in the polymer backbone as described herein may be formed by methods including, without limitation, polymerisation of monomers comprising leaving groups (groups other than H) that leave upon polymerisation of the monomers; oxidative polymerisation; and direct (hetero)arylation. Exemplary leaving groups include, without limitation: halogens, preferably bromine or iodine; sulfonic esters, for example tosylate or mesylate; and boronic acids and esters.

Exemplary polymerisation methods include, without limitation, Yamamoto polymerization as described in, for example, T. Yamamoto, Electrically Conducting And Thermally Stable piConjugated Poly(arylene)s Prepared by Organometallic Processes, Progress in Polymer Science 1993, 17, 1153-1205, the contents of which are incorporated herein by reference; Suzuki polymerization as described in, for example, WO 00/53656, WO 2003/035796, and US 5777070, the contents of which are incorporated herein by reference; and direct (hetero)arylation as disclosed in, for example, Direct (Hetero)arylation Polymerization: Simplicity for Conjugated Polymers Synthesis, Chem. Rev. 2016,116, 14225-14274, the contents of which are incorporated herein by reference.

An n-type or p-type polymer as described herein may be a Schiff base polymer, for example a polymer comprising a repeat unit of formula (X):

(X)

2 wherein R and R are each independently selected from H or a substituent, optionally H, Ci_ 20 alkyl, and C1-20 alkoxy; and Ar and Ar are each independently a C6-20 aromatic or heteroaromatic group, preferably a C6-20 arylene, optionally phenylene.

n-type and p-type polymers as described herein preferably have a polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography in the range of about 1x10 to 1x10 , and more preferably 1x10 to 5x10 . The polystyreneequivalent weight-average molecular weight (Mw) of the n-type and p-type polymers described herein may be 1x10 to 1x10 , and preferably 1x10 to 1x10 .

Separator

The separator may be selected from separators known to the skilled person. The separator comprises an electrolyte. The electrolyte may be a liquid, for example a gel comprising an electrolyte solution or a liquid electrolye. The separator may be a solid polymer electrolyte.

The separator may comprise a mesh, for example a polymeric mesh, comprising electrolyte in the pores of the mesh.

Current collectors

The anode and cathode current collectors each independently comprise or consist of a layer of conductive material, for example a metal such as copper or 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. Each current collector may be supported on a suitable substrate, for example a glass or plastic substrate. The substrates may be flexible, particularly for applications in which flexibility of the battery is desirable, and / or to enable use of a roll-to-roll process in battery formation. An exemplary flexible current collector is a metal foil, for example aluminium foil.

Applications

A battery 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.

Examples

Measurements

Square wave voltammetry measurements as described herein may be performed using a CHI660D Electrochemical workstation with software (U Cambria Scientific Ltd)), a CHI 104 3mm glassy carbon disk working electrode (IJ Cambria Scientific Ltd)); a platinum wire auxiliary electrode; an Ag/AgCl reference electrode (Havard Apparatus Ltd); acetonitrile as cell solution solvent (Hi-dry anhydrous grade-ROMIL); toluene as sample preparation solvent (Hi-dry anhydrous grade); ferrocene as reference standard (FLUKA); and tetrabutylammoniumhexafluorophosphate (FLUKA) as cell solution salt. For sample preparation, the polymer is spun as thin film (~20 nm) onto the working electrode. The measurement cell contains the electrolyte, a glassy carbon working electrode onto which the sample is coated as a thin film, a platinum counter electrode, and a Ag/AgCl reference glass electrode. Ferrocene is added into the cell at the end of the experiment as reference material (LUMO (ferrocene) = -4.8eV).

Formulation Examples

Formulations for forming n-type or p-type first electrode films or additional electrode films were formed by mixing n-type polymer F8BT or p-type polymer F8TFB respectively with Super P Conductive Carbon obtained from Imerys Graphite & Carbon and ionic liquid 1Butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI) obtained from Solvionic in a Polymer : Carbon : Ionic Liquid weight ratio of 1.0 : 0.8 : 0.2.

120 mg of polymer was dissolved in 10 mL of o-dichlorobenzne using a stirrer bar on a hotplate (70°C, 500RPM) until a homogenous solution was obtained. 96 mg of Super P carbon was added and the suspension was stirred for a further 30 minutes. Using a micropipette, 17 microlitres of BMP-TFSI was added and the suspension was stirred for 30 minutes.

Table 1

Polymer	HOMO (eV)	LUMO (eV)	Capacity (mAh/g)	Type
F8BT	-5.85	-2.91	51	n-type
F8TFB	-5.2	-.20	37.6	P-type

The polymer specific capacity (mAh/g) is calculated by dividing the measured capacity

2 (mAh/cm ) by the redox polymer loading (g/cm ).

n-cy-ii7 n-cy-^7

F8TFB

Freestanding further electrode films

Freestanding n-type and p-type electrode layers without a mesh were formed from the formulations described above.

In each case, 3ml of the formulation suspension was pipetted onto a smooth 2x2 inch substrate of Al on glass which was placed on a hotplate at 70°C. The formulation was allowed to dry to form a 40 micron thick film and was then removed from the substrate.

The films were cut to a 1 x 1.5 cm area, transferred to a glovebox and baked at 150°C for 30 minutes to remove any residual moisture.

Freestanding first electrode films

A stainless steel mesh having a wire thickness of 25 microns and a pore size of 40 microns (giving a porosity of 38%) was secured to a 2 x 2 inch substrate of aluminium on glass and the substrate and mesh were placed on a hotplate at 70°C. 1.5 mL of a formulation described above was pipetted onto the mesh, ensuring complete coverage of the mesh with the formulation. The formulation was allowed to dry. Another 1.5 mL of the formulation described above was pipetted onto the mesh carrying the dried formulation and allowed to dry. The mesh electrode film was detached from the substrate, transferred to a glovebox and baked at 150°C for 30 minutes to remove any residual moisture.

Electrode stack formation

1.00 g of poly(ethylene glycol) methyl ether (PEO), average Mn 20,000, obtained from Sigma-Aldrich, 1.0 mL of tetraglyme (TG) obtained from Sigma Aldrich, 0.21 g of 4 methylbenzophenone (MBP) obtained from Sigma Aldrich and 2.0 mL of 1-Butyl-1methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI) obtained from Solvionic were mixed in a pestle and mortar at 120 °C until the PEO and MBP fully melted and a viscous liquid formed, giving an electrolyte mixture having a PEO(20k) : TG : MBP : BMPTFSI weight ratio of 1:1:0.2:2.8.

A mesh electrode film as described above was placed on a 50 micron thick sheet of polyethylene terephthalate (PET), obtained from 3M, with a surface of the mesh electrode film in which the mesh is visible contacting the PET. The molten electrolyte mixture was deposited across the whole surface of the mesh electrode film on the side that is enriched with the active material. A freestanding electrode film without the mesh was then placed on the structure to form a second electrode layer having edges aligned with the underlying first electrode layer formed from the mesh electrode film. The molten electrolyte mixture was deposited across the whole surface of the second electrode layer, and a third electrode layer was formed as described for the second electrode layer. The molten electrolyte mixture was deposited across the whole surface of the third electrode layer.

A second sheet of PET was applied to the top of the stack which was then squeezed between two hotplates at 120°C to melt the PEO, TG and MBP and to cause any excess of these materials to be squeezed out of the stack.

The stack was passed through a laminating machine at 100°C and then cured with UV light _2 (250 W UVH 255 hand lamp with an iron-doped metal halide lamp, intensity >80 mW cm’ ) for 6 minutes either side under an inert, dry atmosphere.

Both n-type electrode stacks and p-type electrode stacks were formed according to this process.

Separator formation

PEO(lOOk), PEO(20k), tetraglyme, MBP and ionic liquid BMP-TFSI in a 3:1:4:0.8:11.2 weight ratio was prepared by mixing 0.25 g of PEO(20k), 1.0 mL of tetraglyme, 0.21 g of MBP and 2.0 mL of BMP-TFSI in a pestle and mortar at 120 °C until the PEO(20k) fully melted and a viscous liquid formed. 0.75 g of PEO (100k) was added, and the mixture was stirred until the PEO(lOOk) fully melted and highly viscous paste formed.

The molten polymer mix was deposited in a roughly 6 cm diameter circle on the back side of a 50 pm thick sheet of PET.

A 47 mm diameter hydrophilic nylon net filter with a 41.0 pm pore size available from Merck Millipore (part number NY4104700) was placed on top of the deposited molten polymer mixture. Another sheet of PET was placed on top of the nylon mesh.

The PET-polymer-nylon-PET sandwich was pressed between two hot plates heated to 120 °C and then laminated at 100 °C to form a thin film of the melt evenly distributed in the pores of the nylon mesh.

Without removing the PET sheets, the polymer mixture was cured using UV light (250 W _2

UVH 255 hand lamp with an iron-doped metal halide lamp, intensity >80 mW cm’ ) for 6 minutes either side under an inert, dry atmosphere.

The resulting gel/nylon composite separator was cut to size (3x2 cm) and then peeled off the PET substrate to give a film having a thickness of between 40-65 pm.

Battery Example 1

PET-backed Al foil obtained from All Foils was covered with an adhesive-backed insulating layer (obtained from Adhesives Research Inc., product number EL-92734) to ensure no shorting during lamination except for a lead-out area for connection and an anode current collection area. The covered foil was cut to have a 5 cm long lead-out extending from the anode current collection area surrounded by the insulation layer.

The insulating layer was covered with a pressure sensitive adhesive. The n-type electrode stack described above was placed on the current collection area, with the mesh electrode layer contacting the aluminium. The separator described above was placed on the n-type electrode stack and p-type electrode stack described above was placed on the separator and in alignment with the n-typc electrode stack with the mesh electrode layer uppermost. The separator completely covers the current collection area

A PET-backed aluminium having a lamination area large enough to cover the anode collection area and surrounding pressure sensitive adhesive and with a 5 cm long lead-out extending therefrom was placed on the p-type electrode stack so as to contact the mesh electrode layer of this stack and form an anode current collector. The complete structure was fed through a laminator heated to 100 °C to seal the aluminium of the cathode current collector to the pressure-sensitive adhesive.

Pressure sensitive adhesive tabs were placed on both sides of the anode and cathode leadouts, 2cm from the end of each lead-out. The device was placed inside a vacuum bag (127 x 76 mm, obtained from RS Components, product number 182-8792) with ends of the lead-outs extending from the vacuum bag. The bag was evacuated and thermally sealed.

Comparative Battery 1

A battery was formed as described for Battery Example 1 except that a freestanding electrode film without a mesh was used in place of the mesh-containing layer for both the anode and the cathode, i.e. all of the anode and cathode layers were formed from a freestanding electrode film without a mesh.

Batteries were placed in a sealed container under an inert atmosphere and connected to an Arbin battery tester (Model - BT2043).

Test parameters:

_2

- Cathodic current 1.0 mA cm’ (discharge current) _2

- Anodic current 1.0 mA cm’ (charging current)

- Charging potential: 3 V

- High potential hold time: 600 s

- Active area: 1.5 cm

- End voltage: 0 V

The charge-discharge sequence was repeated 100 times, and the midpoint voltage and charge capacity calculated for each cycle. The midpoint voltage is defined as the voltage at z/2, where t is the total discharge time of the battery for a given cycle. Charge capacity (expressed _2 in units of mAh cm’ ) is calculated as the time required to discharge to the end voltage multiplied by the cathodic current, and divided by the active area.

_2

Battery Example 1 had a charge capacity of 0.15 mAh cm’ , a midpoint voltage of 1.9 V, and operated for a full 250 cycles, with a Tso(V) = 88 in which Tso(V) is the time taken for voltage to fall to or below 80% of a maximum measured voltage. With reference to Figure 5, a good, repeatable discharge curve was obtained.

In contrast, Comparative Battery 1 had a charge capacity of 3.4 μΑή cm’² and'with reference to Figure 6, gave a discharge curve with no plateau.

Battery Example 2

A device was prepared as described Battery Example 1 except that the battery was not vacuum sealed.

No charging was observed initially, however 4 discharge cycles were achieved after gently squeezing the device, as shown in Figure 7A. After these 4 cycles, a further squeeze was required for the device to begin charging and discharging again, as shown in Figure 7B. These results indicate that biasing the current collectors towards their respective electrodes, for example by use of a vacuum seal, by lamination or by use of a spring clip or other biasing device , is advantageous in maintaining good contact between the current collector and the conductive mesh.

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 freestanding anode or cathode film comprising a conductive mesh and, respectively, an n-type or p-type electrochemically active polymer wherein at least some of the n-type or p-type electrochemically active polymer is disposed in pores of the conductive mesh.

2. A freestanding electrode film according to claim 1 wherein the electrochemically active polymer is an n-type electrochemically active polymer.

3. A freestanding electrode film according to claim 1 wherein the electrochemically active polymer is a p-type electrochemically active polymer.

4. A freestanding electrode film according to any one of the preceding claims wherein the film comprises a conductive carbon material.

5. A freestanding electrode film according to claim 4 wherein the conductive carbon material is selected from the group consisting of carbon black, carbon fiber, graphite, and carbon nanotubes.

6. A freestanding electrode film according to any one of the preceding claims wherein the film comprises an electrolyte.

7. A freestanding electrode film according to claim 6 wherein the electrolyte is an ionic liquid.

8. A freestanding electrode film according to claim 7 wherein the ionic liquid is 1-butyl1-methyip yrrolidinium bis (trifluoromethane) sulfonimide.

9. A freestanding electrode film according to any one of the preceding claims wherein the film has a thickness in the range of 50-750 microns.

10. A freestanding electrode film according to any one of the preceding claims wherein a surface of the conductive mesh is exposed at a surface of the film.

11. A method of forming a freestanding composite electrode film according to any one of the preceding claims, the method comprising the step of depositing a formulation comprising the n-type or p-type electrochemically active polymer dissolved or dispersed in one or more solvents onto a surface of the conductive mesh supported on a film-forming substrate; evaporating the solvent or solvents to form a film; and separating the film from the film-forming substrate.

12. A battery comprising an anode, a cathode, a separator between the anode and the cathode, an anode current collector and a cathode current collector, wherein the anode comprises a first anode layer comprising a p-type polymer and a conductive mesh in direct contact with the anode current collector or the cathode comprises a first cathode layer comprising an n-type polymer and a conductive mesh in direct contact with the cathode current collector.

13. A battery according to claim 12 wherein the anode comprises the first anode layer and the cathode comprises the first cathode layer.

14. A battery according to claim 12 or 13 wherein the anode comprises at least one additional anode layer or the cathode comprises at least one additional cathode layer.

15. A battery according to any one of claims 12-14 wherein the battery is vacuum sealed in a vacuum pouch.

16. A method of forming a battery according to any one of claims 12-15, wherein the first anode layer or the first cathode layer is formed by lamination of, respectively, a freestanding anode or cathode layer according to any one of claims 1-10.

17. A method according to claim 16 wherein the first anode layer is formed by lamination of the freestanding anode layer and the first cathode layer is formed by lamination of the freestanding cathode layer.

18. A method according to claim 16 or 17 wherein the anode is a stack comprising the first anode layer and one or more additional anode layers or the cathode is a stack comprising the first cathode layer and one or more additional cathode layers, each additional anode or cathode layer being formed by lamination of one or more additional freestanding electrode layers.

19. A method according to claim 18 wherein formation of the anode or cathode stack comprises formation of the first anode or cathode layer by lamination of the freestanding anode or cathode film to the anode current collector or cathode current collector and formation of the one or more additional anode or cathode layers by lamination of one or more additional freestanding anode or cathode layers to the first anode or cathode layers.

20. A battery obtainable by method according to any one of claims 16-19.