Stack for an electrochemical cell

Abstract

A stack for an electrochemical cell has a laminate structure including a first gel separator layer and a second gel separator layer; a solid solvent-cast electrode layer between the first and second gel separator layers; and a gel electrode layer in contact with the first gel separator layer. The stack finds use in electrochemical secondary cells, including lithium ion secondary cells.

Description

[0001] STACK FOR AN ELECTROCHEMICAL CELL

[0002] Field of the Invention

[0003] The present invention relates to a stack for an electrochemical cell, electrochemical cells comprising such stacks, and energy storage devices containing such cells.

[0004] Background of the Invention

[0005] Lithium-ion secondary batteries are the leading battery technology currently used in applications from small personal devices to electric vehicles. Lithium-ion batteries are favoured for their high energy density and long cycle life, among other benefits. They contain a plurality of lithium-ion secondary cells, which is one example of an alkali metal ion secondary cell.

[0006] Traditional lithium-ion battery components such as electrodes are made from a solvent cast process that uses sacrificial solvent. This is an energetically expensive step, and a process that avoids using sacrificial solvent is therefore desirable.

[0007] A further major drawback of lithium-ion technology and other alkali-metal ion secondary cell technology is that a liquid electrolyte is often used within the lithium-ion cells of the battery, to provide conductivity of lithium ions within the cell between the solid, solvent cast anode and cathode. This causes safety problems since the liquid electrolytes are often highly flammable. This is a particular problem for electric vehicles, where a collision with another vehicle may be relatively likely and the resulting impact may cause damage to the battery and ignition of the electrolyte. It is also a problem for devices used in the home, where a lithium-ion battery fire could cause damage to property or serious injury.

[0008] One approach to avoiding the use of sacrificial solvent, and the need for liquid electrolyte within the cell, is preparing gel electrodes. These electrodes can be formed from a composition prepared by mixing the necessary components such as electrochemically active material, polymer, and a liquid electrolyte, and subsequently subjecting the composition to a thermal treatment. Such gel electrodes are described in WO 2017 / 017023 Al, which attempts to manufacture electrochemical devices free of liquid electrolytes.

[0009] Although gel electrodes offer advantages over more conventional electrode chemistry, they also present some problems. Firstly, manufacturing a gel electrode requires thermal processing, which may be detrimental to some of the ingredients within the electrode. Secondly, the range of electrolytes which may be compatible with the components of the gel electrode may be limited, limiting the versatility of the cell. For example, certain high-rate performance electrolytes may be incompatible for use within a gel electrode due to the thermal processing required or the need to be able to coexist with the gelled polymer component.

[0010] There is a need for a stack (i.e. layered combination of electrodes and separator) which addresses these problems with gel electrodes while still delivering their benefits to the finished cell.

[0011] Summary of the Invention

[0012] The invention relates generally to a stack for an electrochemical cell, e.g. an electrochemical secondary cell, and more specifically to a stack having a laminate structure comprising a first gel separator layer, a second gel separator layer, a solid solvent-cast electrode layer and a gel electrode layer.

[0013] A first aspect of the invention is a stack for an electrochemical cell, having a laminate structure comprising: a first gel separator layer and a second gel separator layer; a solid solvent-cast electrode layer between the first and second gel separator layers; and a gel electrode layer in contact with the first gel separator layer.

[0014] The stack of the first aspect contains a solid solvent-cast electrode layer between first and second gel separator layers. The stack also contains a gel electrode layer in contact with the first gel separator layer.

[0015] The gel electrode layer contains a polymer-electrolyte gel matrix phase and a dispersed phase of solid particulate material dispersed through the matrix phase. In this way, the electrode has a gel-like composition, where the electrode structure contains liquid electrolyte trapped within the matrix phase due to the gelled nature of the polymer. The presence of such gel electrodes reduces fire risk and provides a stack of increased safety when used within a cell.

[0016] Similarly, the first and second gel separator layers each have a gel-like composition, where the separator structure contains liquid electrolyte trapped within a matrix phase due to the gelled nature of the polymer. This further improves the safety of the stack when used within a cell, reducing fire risk. However, the cell also contains a solid solvent-cast electrode layer between the first and second gel separator layers. In this way, greater versatility is provided, since certain components, e.g. electrochemically active materials, which would not be suitable for use within a gel electrode may nevertheless be used in the stack within the solvent-cast electrode layer. For example, components which could be damaged or detrimentally impacted by the thermal processing which is necessary to form a gel electrode could still be utilised within the solid solvent-cast electrode layer, thereby increasing the range of components which could be used while still delivering the benefits provided by the remaining, gelled layers of the stack.

[0017] Furthermore, after assembly of the stack of the first aspect into a cell, it is possible to introduce further liquid electrolyte to “wet” into the solid solvent-cast electrode layer (“filling electrolyte”) and provide ionic conductivity within the cell. Such an electrolyte could be chosen from a wide range of electrolytes, including those which may not have been suitable to include within the gel electrode or gel separators (e.g. due to immiscibility with the gelling polymers used). As a result, a more versatile cell is possible containing e.g. sensitive high-rate electrolytes compositions within the solid solventcast electrode layer which may provide a cell with higher rate capability than would otherwise be possible with e.g. a fully gelled cell.

[0018] The stack of the invention therefore achieves a compromise between operational safety and versatility.

[0019] A second aspect of the invention provides an electrochemical secondary cell, e.g. a lithium ion electrochemical secondary cell, comprising a stack according to the first aspect.

[0020] The benefits of the stack described above will be appreciated when it is assembled into a complete electrochemical secondary cell and used to reversibly store electrical energy.

[0021] The use of the stack in the cell of the second aspect provides safety benefits due to the reduced flammability of the cell and also provides greater versatility due to the presence of the solid solventcast electrode layer.

[0022] In some embodiments, the cell further comprises free electrolyte. In some embodiments, the free electrolyte permeates the free space around and between the components of the cell, including the electrodes and the separators, thereby providing ionic conductivity across the separators between the electrodes. In some embodiments the free electrolyte within the cell has a composition which differs from the composition of the electrolyte within the polymer-electrolyte gel matrix phase of the electrode. In this way, the electrolyte within the polymer-electrolyte gel matrix phase may be tailored for the gelation and functioning of the gel electrode while the free electrolyte within the cell can may be tailored for one or more of ionic conductivity, rate capability, the filling of free space within the cell and the reduction of tortuosity. In other embodiments the free electrolyte within the cell has a composition identical with the composition of the electrolyte within the polymer-electrolyte gel matrix phase of the electrode. In this way manufacture of the cell is simplified with a single electrolyte composition used throughout.

[0023] A third aspect of the invention is an electrochemical energy storage device comprising an electrochemical cell according to the second aspect.

[0024] A fourth aspect of the invention is a method of manufacturing the stack according to the first aspect, the method comprising: positioning a solid solvent-cast electrode layer between a first gel separator layer and a second gel separator layer; and placing a gel electrode layer into contact with the first gel separator layer.

[0025] Preferred and / or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and / or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise.

[0026] Solid solvent-cast electrode layer

[0027] In some embodiments, the solid solvent-cast electrode layer comprises an electrochemically active material layer deposited on a foil current collector layer.

[0028] In some embodiments, the foil current collector layer comprises aluminium, copper or carbon fibre. In some embodiments, the foil current collector layer comprises a metal current collector layer coated with a primer layer. In some embodiments, the primer layer comprises conductive carbon. The primer layer may help to reduce the interfacial resistance between the metal current collector layer and the solid solvent-cast electrode layer. The primer layer will form an interlayer between the metal current collector layer and the solid solvent-cast electrode layer. In some embodiments, the metal current collector layer comprises or consists of copper or aluminium.

[0029] In some embodiments, the solid solvent-cast electrode layer comprises particulate electrochemically active material, optionally a conductive additive, and optionally a binder. In some embodiments, the solid solvent-cast electrode layer comprises particulate electrochemically active material, a conductive additive, and optionally a binder. In some embodiments, the solid solvent-cast electrode layer comprises particulate electrochemically active material, a conductive additive, and a binder. In some embodiments, the solid solvent-cast electrode layer is impregnated with free liquid electrolyte. In some embodiments, the free liquid electrolyte comprises a linear or cyclic carbonate liquid electrolyte and one or more lithium salts.

[0030] In some embodiments the conductive additive comprises one or more of carbon black and graphite. In some embodiments, the conductive additive comprises or consists of carbon black.

[0031] In some embodiments the conductive additive comprises carbon nanotubes, for example single wall carbon nanotubes (SWCNTs) or multiwall carbon nanotubes (MWCNTs).

[0032] In some embodiments the conductive additive comprises or consists of one or more of carbon black and graphite.

[0033] Examples of commercially available carbon black include Ketjen Black and Super C65.

[0034] The binder may comprise one or more polymers. In some embodiments, the binder comprises one or more polymers independently selected from poly(ethyleneglycol dimethacrylate), poly(ethyleneglycol diacrylate), poly(propyleneglycol dimethacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (PU), poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP), poly(ethylene oxide) (PEO), poly-L-lactic acid (PLA), polystyrene (PS), poly(ethyleneglycol dimethylether), poly(ethyleneglycol diethylether), poly[bis(methoxy ethoxyethoxide)-phosphazene], poly(dimethylsiloxane) (PDMS), polyacene, polydisulfide, polystyrene, polystyrene sulfonate, polypyrrole, polyaniline, polythiophene, polythione, polyvinyl pyridine (PVP), polyvinyl chloride (PVC), polyaniline, poly(3,4- ethylenedioxythiophene) (PEDOT), poly(p-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiafulvalenesubstituted polystyrene, ferrocene-substituted polyethylene, carbazole-substituted polyethylene, poly oxyphenazine, poly(heteroacene), poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide-co- methoxy-polyethyleneglycolacrylate] (Li[PSTFSI-co-MPEGA]), sulfonated poly(phenylene oxide) (PPO), N,N-dimethylacryl amide (DMAAm), lithium 2-acrylamido-2 -methyl- 1 -propane sulfonate (LiAMPS), Poly(lithium 2-Acrylamido-2 -Methylpropanesulfonic Acid-Co-Vinyl Triethoxysilane), polyethyleneoxide(PEO) / poly(lithium sorbate), PEO / poly(lithium muconate), PEO / [poly(lithium sorbate)+BF3], PEO copolymer, PEO terpolymer, and NIPPON SHOKUBAI® polymer.

[0035] In some embodiments, the binder comprises a cellulosic polymer, for example carboxymethylcellulose (CMC). In some embodiments, the solid solvent-cast electrode layer is a solid solvent-cast anode layer. In such embodiments, the gel electrode layer will be a gel cathode layer. Particular advantages are achieved when the solid solvent-cast electrode layer is a solid solvent-cast anode layer. It has been found by the inventors that the components of an anode composition are relatively difficult to successfully form into a gel electrode, and may be less suitable for forming into a gel electrode than the corresponding components of a cathode composition. As such, a stack which includes a gel anode layer may be more difficult to manufacture and / or less stable during use. By providing a solid solvent-cast anode layer in the stack instead of a gel anode layer, the benefits of gel components are delivered by the gel separator layers and gel cathode layer, while avoiding the difficulties associated with the manufacture of gel anodes.

[0036] The particulate electrochemically active material may be a particulate positive active material (if the solid solvent-cast electrode layer is a cathode layer) or a particulate negative active material (if the solid solvent-cast electrode layer is an anode layer).

[0037] In some embodiments, solid solvent-cast electrode layer is a solid solvent-cast anode layer comprising particulate negative active material, optionally a conductive additive, and optionally a binder. In some embodiments, the solid solvent-cast anode layer comprises particulate negative active material, a conductive additive, and a binder.

[0038] In some cases, the negative active material may comprise carbon, suitably graphite, graphene or a blend of carbon and a silicon oxide. In some embodiments, the negative active material is selected from one or more of graphite, silicon, silicon oxide, prelithiated silicon oxide and SiC composites.

[0039] In embodiments where the solid solvent-cast electrode layer is a solid solvent-cast cathode layer, the solid solvent-cast cathode layer may comprise particulate positive active material, optionally a conductive additive, and optionally a binder. In such embodiments, the gel electrode layer will be a gel anode layer. The positive active material in the solid, solvent-cast cathode may be selected from one or more of lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel cobalt oxide (NCO), aluminium-doped lithium nickel cobalt oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium nickel oxide (LNO), lithium nickel manganese oxide (LNMO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LFP) and lithium nickel vanadate (LNV).

[0040] The solid, solvent-cast electrode layer may be manufactured by methods known to the skilled person which generally include the preparation of a slurry comprising the positive active material and the conductive additive, along with any further optional ingredients, in a solvent; casting the slurry onto a substrate and drying to remove the solvent. In some embodiments, the solid components of the solid, solvent-cast electrode layer are dispersed in water to form a slurry, cast onto a substrate and dried to remove the water. Using water as the solvent makes the process more environmentally friendly.

[0041] In some embodiments, the solid components of the solid, solvent-cast electrode layer are dispersed in the solvent to form a slurry, cast onto a foil current collector layer and dried to remove the water. In some embodiments, this process is performed to deposit an electrode layer onto a first side of a foil current collector layer, and then after drying the process is repeated to subsequently deposit an electrode layer onto a second side of the foil current collector layer. In this way, a foil (e.g. copper or aluminium) current collector layer is formed which carries an electrode layer on both sides. Such a double-sided electrode layer with a central current collector layer may alternatively be formed by tandem casting, i.e. depositing a slurry onto both sides of the foil simultaneously before drying to remove the solvent.

[0042] Gel electrode layer

[0043] In some embodiments, the gel electrode layer is a gel cathode layer. In such embodiments, the solid solvent-cast electrode layer is a solid solvent-cast anode layer, as discussed above.

[0044] In some embodiments, the gel electrode layer comprises a polymer-electrolyte gel matrix phase; and a dispersed phase comprising a positive active material.

[0045] In some embodiments, the dispersed phase of the gel cathode layer makes up from 80 to 90 wt% of the gel cathode layer, for example from 82 to 88 wt%, from 85 to 88 wt% or from 85 to 86 wt%.

[0046] In some embodiments, the positive active material makes up at least 50 vol% of the gel cathode layer, for example at least 55 vol%, at least 60 vol%, at least 62 vol%, at least 64 vol%, at least 65 vol%, at least 66 vol%, at least 67 vol% or at least 68 vol%.

[0047] In some embodiments the positive active material makes up from 50 to 75 vol% of the gel cathode layer, for example from 50 to 70 vol%, from 50 to 69 vol%, from 50 to 68 vol%, from 55 to 68 vol%, from 58 to 68 vol% or from 60 to 68 vol%.

[0048] In some embodiments the positive active material makes up from 62 to 75 vol% of the gel cathode layer, for example from 62 to 70 vol%, from 62 to 69 vol%, from 62 to 68 vol% or from 64 to 69 vol%. In some embodiments the gel cathode layer comprises a conductive additive.

[0049] In some embodiments the dispersed phase of the cathode of the first aspect comprises the conductive additive.

[0050] In some embodiments the conductive additive comprises one or more of carbon black and graphite. In some embodiments, the conductive additive comprises or consists of carbon black. Examples of commercially available carbon black include Ketjen Black and Super C65.

[0051] In some embodiments the conductive additive comprises carbon nanotubes, for example single wall carbon nanotubes (SWCNTs) or multiwall carbon nanotubes (MWCNTs).

[0052] In some embodiments the conductive additive comprises or consists of one or more of carbon black and graphite.

[0053] In some embodiments, the conductive additive is present in an amount of from 0.5 wt% to 2.5 wt%, based on the total weight of the gel cathode layer.

[0054] In some embodiments, the first conductive additive is present in an amount of from 1.5 vol% to 2.5 vol%, based on the total weight of the gel cathode layer, for example from 1.5 vol% to 2.5 vol%, from 1.5 vol% to 2.4 vol%, from 1.5 vol% to 2.3 vol%, from 1.5 vol% to 2.2 vol%, from 1.5 vol% to 2.1 vol% or from 1.6 vol% to 2. 1 vol%.

[0055] In some embodiments, the dispersed phase of the gel cathode layer comprises from 2 vol% to 4 vol% positive active material, based on the total volume of the dispersed phase of the gel cathode layer, for example from 2. 1 vol% to 3.9 vol%, from 2.2 vol% to 3.8 vol%, from 2.3 vol% to 3.7 vol%, from 2.3 vol% to 3.6 vol%, from 2.3 vol% to 3.5 vol% or from 2.4 vol% to 3.5 vol%.

[0056] In some embodiments, the dispersed phase of the gel cathode layer comprises from 96 vol% to 98 vol% positive active material, based on the total volume of the dispersed phase of the gel cathode layer, for example from 96.1 vol% to 97.9 vol%, from 96.2 vol% to 97.8 vol%, from 96.3 vol% to 97.7 vol%, from 96.3 vol% to 97.6 vol%, from 96.3 vol% to 97.5 vol% or from 96.4 vol% to 97.5 vol%.

[0057] In some embodiments the dispersed phase of the gel cathode layer comprises from 98.5 to 99.5 wt% positive active material, for example from 98.8 to 99.5 wt%, from 99.0 to 99.5 wt%, or from 99. 1 to 99.3 wt%, based on the total weight of the dispersed phase. The dispersed phase of the gel cathode layer may consist of the positive active material and the conductive additive. In some embodiments the dispersed phase consists of the positive active material and carbon black.

[0058] In some embodiments the dispersed phase of the gel cathode layer comprises from 0.5 to 1.5 wt% first conductive additive, for example from 0.5 to 1.0 wt%, from 0.6 to 1.0 wt%, or from 0.7 to 0.9 wt%.

[0059] In some embodiments, the dispersed phase of the gel cathode layer consists of the positive active material and the first conductive additive.

[0060] In some embodiments, the polymer-electrolyte gel matrix phase of the gel cathode layer comprises a mixture of a gelling polymer and a liquid electrolyte. In some embodiments, the polymer-electrolyte gel matrix phase comprises a mixture of a gelling polymer and a liquid electrolyte, wherein the weight ratio of electrolyte: polymer is from 2 to 8, for example from 3 to 8, from 4 to 8 or from 5 to 7. In some embodiments, the polymer-electrolyte gel matrix phase consists of the gelling polymer and the liquid electrolyte.

[0061] In some embodiments, the gel cathode layer comprises a gelling polymer in an amount of from 5 to 10 vol%, based on the total volume of gel cathode layer, for example from 5 to 9 vol%, from 5 to 8 vol%, from 5.5 to 8 vol% or from 6 to 8 vol%.

[0062] In some embodiments, the gel cathode layer comprises a gelling polymer in an amount of from 0.5 to 5 wt%, based on the total weight of cathode, for example from 0.5 to 3 wt%, from 1.0 to 3 wt%, from 1.5 to 3 wt% or from 1.5 to 2.5 wt%.

[0063] In some embodiments, the polymer-electrolyte gel matrix phase of the gel cathode layer comprises the gelling polymer in an amount of from 15 to 25 vol%, based on the total volume of polymer-electrolyte gel matrix phase, for example from 15 to 24 vol%, from 16 to 24 vol%, from 17 to 24 vol%, from 17 to 23 vol%, from 18 to 23 vol%, from 18 to 22 vol%, from 19 to 22 vol%, from 19 to 21 vol%, or about 20 vol%.

[0064] In some embodiments the polymer-electrolyte gel matrix phase comprises 10 to 20 wt% gelling polymer, based on the total weight of first polymer-electrolyte gel matrix phase, for example from 10 to 18 wt%, from 10 to 16 wt% or from 12 to 14 wt%. In some embodiments, the polymer-electrolyte gel matrix phase of the gel cathode layer comprises the electrolyte in an amount of from 75 to 85 vol%, based on the total volume of polymer-electrolyte gel matrix phase, for example from 75 to 84 vol%, from 76 to 86 vol%, from 77 to 84 vol%, from 77 to 83 vol%, from 78 to 83 vol%, from 78 to 82 vol%, from 79 to 82 vol%, from 79 to 81 vol%, or about 80 vol%.

[0065] In some embodiments the polymer-electrolyte gel matrix phase comprises 80 to 90 wt% electrolyte, based on the total weight of polymer-electrolyte gel matrix phase, for example from 82 to 88 wt%, from 84 to 88 wt% or from 85 to 87 wt%.

[0066] In some embodiments, the gel cathode layer comprises the electrolyte in an amount of from 20 to 35 vol%, based on the total volume of the gel cathode layer, for example from 21 to 34 vol%, from 22 to 33 vol%, from 23 to 32 vol% or from 24 to 31 vol%.

[0067] In some embodiments, the gel cathode layer comprises the electrolyte in an amount of from 10 to 15 wt%, based on the total weight of the gel cathode layer, for example from 11 to 15 wt%, from 11 to 14 wt%, or from 11 to 13 wt%.

[0068] In some embodiments, the polymer-electrolyte gel matrix phase of the gel cathode layer makes up from 20 vol% to 50 vol% of the cathode, for example from 25 vol% to 45 vol%, from 28 vol% to 42 vol%, from 30 vol% to 40 vol%, from 31 vol% to 49 vol% or from 32 vol% to 48 vol%.

[0069] In some embodiments the gel cathode layer comprises from 10 to 20 wt% first polymer-electrolyte gel matrix phase, based on the total gel cathode layer weight, for example from 11 to 17 wt%, from 12 to 16 wt% or from 13 to 15 wt%.

[0070] The identity of the electrochemically active material in the gel cathode layer is not of particular importance. The benefits of the invention may be achieved for any active material which could be present in an electrode. The skilled person will be aware of a large number of possible cathode active materials (also called positive active materials) and anode active materials (also called negative active materials) which may be used in the present invention.

[0071] The positive and negative active materials are each particulate materials, i.e. materials made up of a plurality of discrete particles. The particles may comprise primary particles and / or secondary particles formed from the agglomeration of a plurality of primary particles. In some embodiments, the positive active material is a lithium transition metal oxide material. In some embodiments, the positive active material is a lithium transition metal oxide material comprising a mixed metal oxide of lithium and one or more transition metals, optionally further comprising one or more additional non-transition metals. In some embodiments, the positive active material is a lithium transition metal oxide material comprising lithium and one or more transition metals selected from nickel, cobalt and manganese. In some embodiments, the positive active material is selected from one or more of lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel cobalt oxide (NCO), aluminium-doped lithium nickel cobalt oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium nickel oxide (LNO), lithium nickel manganese oxide (LNMO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LFP) and lithium nickel vanadate (LNV). In some embodiments, the positive active material is lithium nickel manganese cobalt oxide (NMC), optionally doped with another metal such as aluminium.

[0072] Such positive active materials are commercially available or may be manufactured by methods known to the skilled person, for example through the precipitation of mixed metal hydroxide intermediates from a reaction mixture containing different precursor metal salts, followed by calcination to form a mixed metal oxide and optionally lithiation to incorporate lithium into the oxide.

[0073] The positive active material may be undoped or uncoated, or may contain one or more dopants and / or a coating. For example, the positive active material may be doped with small amounts of one or more metal elements. The positive active material may comprise a carbon coating on the surface of the particles of the material.

[0074] In embodiments where the gel electrode layer is a gel anode layer, a negative active material will instead be chosen, and may be selected from those already mentioned above.

[0075] In some embodiments, the gel electrode layer comprises one or more polymers independently selected from poly (ethyleneglycol dimethacrylate), poly (ethyleneglycol diacrylate), poly (propyleneglycol dimethacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (PU), poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP), polyethylene oxide) (PEO), poly-L-lactic acid (PLA), polystyrene (PS), poly(ethyleneglycol dimethylether), poly(ethyleneglycol diethylether), poly[bis(methoxy ethoxyethoxide)-phosphazene], poly(dimethylsiloxane) (PDMS), polyacene, polydisulfide, polystyrene, polystyrene sulfonate, polypyrrole, polyaniline, polythiophene, polythione, polyvinyl pyridine (PVP), polyvinyl chloride (PVC), polyaniline, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiafulvalene-substituted polystyrene, ferrocene- substituted polyethylene, carbazole-substituted polyethylene, poly oxyphenazine, poly(heteroacene), poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide-co-methoxy-polyethyleneglycolacrylate] (Li[PSTFSI-co-MPEGA]), sulfonated poly(phenylene oxide) (PPO), N,N-dimethylacryl amide (DMAAm), lithium 2 -acrylamido-2 -methyl- 1 -propane sulfonate (LiAMPS), Poly(lithium 2- Acrylamido-2 -Methylpropane sulfonic Acid-Co-Vinyl Triethoxysilane), polyethyleneoxide(PEO) / poly(lithium sorbate), PEO / poly(lithium muconate), PEO / [poly(lithium sorbate)+BF3], PEO copolymer, PEO terpolymer, and NIPPON SHOKUBAI® polymer.

[0076] In some embodiments, the gel electrode layer comprises one or more polymers independently selected from poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF- HFP), poly(methyl methacrylate) (PMMA), polyethylene oxide) (PEO), poly-L-lactic acid (PLA) and polystyrene (PS).

[0077] In some embodiments, the gel electrode layer further comprises a linear or cyclic carbonate liquid electrolyte, one or more lithium salts and an electrochemically active material.

[0078] In some embodiments, the gel electrode layer is an extruded gel electrode layer. In other embodiments, the gel electrode layer is a hot-rolled gel electrode layer. In other embodiments, the gel electrode layer is prepared by extruding an electrode precursor composition through a die to form a fdm.

[0079] In some embodiments the gel electrode layer is formed by one or more hot-rolling steps carried out on an electrode precursor composition, followed by one or more extrusion steps.

[0080] In some embodiments the gel electrode layer has athickness of less than 150 pm, for example less than 100 pm, less than 90 pm, less than 80 pm or less than 70 pm. In some embodiments the gel electrode layer has a thickness of from 40 to 150 pm, for example from 40 to 100 pm, from 40 to 90 pm, from 40 to 80 pm, from 40 to 70 pm or from 50 to 70 pm.

[0081] In some embodiments the gel electrode layer has athickness of from 40 to 150 pm, for example from 40 to 100 pm, from 40 to 90 pm, from 40 to 80 pm, from 40 to 70 pm or from 50 to 70 pm, and comprises the electrochemically active material in an amount of from 50 to 75 vol% of the gel electrode layer, for example from 55 to 70 vol%, from 60 to 69 vol%, from 62 to 68 vol% or from 64 to 69 vol%.

[0082] In some embodiments the gel electrode layer has a porosity of less than about 5% by volume. In some cases, the porosity of the gel electrode layer is less than 5 vol%, less than 3 vol% or less than 2 vol%. To phrase in another manner, the volumetric density of the gel electrode layer may be at least 95%, suitably at least about 97% or 98% of the density of a perfectly non-porous gel electrode layer.

[0083] In some cases, the extruded gel electrode layer may form part of an extruded monolith which includes one or more further layers which are present in an electrochemical battery. For instance, the monolith may include a separator layer, and / or may include another gel electrode layer of opposite polarity (i.e. the extruded monolith may include both a cathode and anode). The different layers may be coextruded and have different compositions from one another.

[0084] In some embodiments, the gel electrode layer is supported upon a foil current collector layer. In some embodiments, the foil current collector layer comprises aluminium, copper or carbon fibre. In some embodiments, the foil current collector layer comprises or consists of aluminium. In some embodiments, the foil current collector layer comprises a metal current collector layer coated with a primer layer. In some embodiments, the primer layer comprises conductive carbon. The primer layer may help to reduce the interfacial resistance between the metal current collector layer and the solid solvent-cast electrode layer. The primer layer will form an interlayer between the metal current collector layer and the solid solvent-cast electrode layer. In some embodiments, the metal current collector layer comprises or consists of copper or aluminium.

[0085] In some embodiments, the gel electrode layer is supported upon a first side of a foil current collector layer and a further gel electrode layer is supported upon a second side of the foil current collector layer. In this way, a foil current collector layer (e.g. aluminium current collector) is provided having gel electrode layers supported on both sides. In some embodiments, the two gel electrode layers are the same as one another, e.g. the gel cathode layers as described above. In this way, a battery of cells can be easily built up as individual stacks as described herein are placed in contact with one another, with current collector layers already in place.

[0086] The gel electrode layer may be supported upon the foil current collector layer by extruding the gel electrode directly onto the foil current collector layer, for example by applying an electrode precursor composition onto the foil current collector layer before performing one or more hot-rolling steps and / or one or more extrusion steps, to form the supported gel electrode layer.

[0087] Alternatively, the gel electrode layer may be formed separately by the extrusion or hot rolling steps described above, followed by application of the gel electrode layer onto the foil current collector layer. First and second gel separator layers

[0088] In some embodiments, the first and second gel separator layers each independently comprise one or more polymers independently selected from poly(ethyleneglycol dimethacrylate), poly(ethyleneglycol diacrylate), poly(propyleneglycol dimethacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (PU), poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP), poly(ethylene oxide) (PEO), poly-L-lactic acid (PLA), polystyrene (PS), poly(ethyleneglycol dimethylether), poly(ethyleneglycol diethylether), poly[bis(methoxy ethoxyethoxide)-phosphazene], poly(dimethylsiloxane) (PDMS), polyacene, polydisulfide, polystyrene, polystyrene sulfonate, polypyrrole, polyaniline, polythiophene, polythione, polyvinyl pyridine (PVP), polyvinyl chloride (PVC), polyaniline, poly(3,4- ethylenedioxythiophene) (PEDOT), poly(p-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiafulvalene- substituted polystyrene, ferrocene-substituted polyethylene, carbazole-substituted polyethylene, poly oxyphenazine, poly(heteroacene), poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide-co- methoxy-polyethyleneglycolacrylate] (Li[PSTFSI-co-MPEGA]), sulfonated poly(phenylene oxide) (PPO), N,N-dimethylacryl amide (DMAAm), lithium 2-acrylamido-2 -methyl- 1 -propane sulfonate (LiAMPS), Poly(lithium 2-Acrylamido-2 -Methylpropanesulfonic Acid-Co-Vinyl Triethoxysilane), polyethyleneoxide(PEO) / poly(lithium sorbate), PEO / poly(lithium muconate), PEO / [poly(lithium sorbate)+BF3], PEO copolymer, PEO terpolymer, and NIPPON SHOKUBAI® polymer.

[0089] In some embodiments, the first and second gel separator layers each independently comprise one or more polymers independently selected from poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP), poly(methyl methacrylate) (PMMA), polyethylene oxide) (PEO), poly-L-lactic acid (PLA) and polystyrene (PS).

[0090] These polymers have been found to provide the combined benefits of good electrochemical properties alongside good heat-sealing properties.

[0091] In some embodiments, the first and second gel separator layers and the first electrode layer each independently comprise one or more polymers independently selected from poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP), poly(methyl methacrylate) (PMMA), polyethylene oxide) (PEO), poly-L-lactic acid (PLA) and polystyrene (PS). In some embodiments, the first and second gel separator layers and the first electrode layer each independently comprise one or more polymers independently selected from poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP) and poly(methyl methacrylate) (PMMA). In some embodiments, the first and second gel separator layers and the first electrode layer each independently comprise one or more polymers independently selected from poly(vinylidene difluoride) (PVdF) and poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF- HFP).

[0092] In some embodiments, the first and second gel separator layers each independently further comprise a liquid electrolyte. In some embodiments, the first and second gel separator layers each independently further comprise a liquid electrolyte and a lithium salt.

[0093] The liquid electrolyte causes gelation of the polymer to form the first and second gel separator layers. In some embodiments, the liquid electrolyte comprises a linear or cyclic carbonate solvent and a lithium salt. In some embodiments the solvent comprises or consists of one or more of ethylene carbonate (EC) propylene carbonate (PC), vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0094] In some embodiments, the lithium salt comprises one or more of LiPFg, LiBF4, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium 4,5- dicyano-2-(trifluoromethyl)imidazolide (LiTDI), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorophosphate and lithium bis(oxalato) borate. In some embodiments, the liquid electrolyte comprises a mixture of two or more different lithium salts.

[0095] In some embodiments, the first and second gel separator layers further comprise a linear or cyclic carbonate liquid electrolyte and one or more lithium salts.

[0096] In some embodiments, the first gel separator layer and second gel separator layer each extend beyond the peripheral edge of the solid solvent-cast electrode layer around the entire peripheral edge of the solid solvent-cast electrode layer.

[0097] In some embodiments, the first gel separator layer and second gel separator layer are adhered to one another by a heat-sealed border region which extends around the periphery of the solid solvent-cast electrode layer.

[0098] In some embodiments, the first gel separator layer and second gel separator layer are adhered to one another and to the solid solvent-cast electrode layer by a heat seal across the internal faces of the first gel separator layer and second gel separator layer.

[0099] In some embodiments, the first and second gel separator layers each independently have a thickness of from 10 to 30 pm. Stack for an electrochemical cell

[0100] The above-described layers are assembled together to form the stack for an electrochemical cell. The term “stack” is known to the skilled person and refers to the assembly of components or elements which together form a cell assembly or cell subassembly. The stack can be further manipulated or combined with further components to form a complete electrochemical cell.

[0101] In some embodiments, the first gel separator layer and second gel separator layer each extend beyond a peripheral edge of the solid solvent-cast electrode layer such that they contact one another beyond the peripheral edge of the first electrode layer. In this way, the solid solvent-cast electrode layer is fully enclosed or enveloped within the two gel separator layers. This reduces the risk of the solid solvent-cast electrode layer coming into contact with another electrode layer, which could cause a short-circuit within a cell containing the stack. To achieve this arrangement, the first gel separator layer and second gel separator layer may each have a surface area which is greater than the surface area of the solid solvent-cast electrode layer, such that, when the three layers are assembled together, the first gel separator layer and second gel separator layer extend beyond the solid solvent-cast electrode layer around its entire periphery.

[0102] The layers making up the stack may be either “actively” or “passively” adhered together. In this context, “passive” adherence refers to the layers being simply assembled by placing the layers into contact with one another, optionally with applied pressure. Since the stack comprises gel layers (first gel separator layer, second gel separator layer and gel electrode layer), there will be some natural tackiness associated with these layers that will provide some minimal level of adherence between adjacent layers. As such, further methods of adhering layers together may not be performed and this “passive” adhesion between the layers is used to keep the layers within the assembly in position relative to one another.

[0103] However the inventors have found that such “passive” adhesion may cause problems in some cases. For instance, layers may move relative to one another after assembly of the stack where only “passive” adhesion holds them together, which could lead to a short-circuit of a cell comprising the stack if the anode and cathode come into contact.

[0104] As a result, in some embodiments two or more adjacent layers within the stack may be “actively” adhered to one another. In some embodiments, “active” adhesion comprises a heat-seal between the two or more layers. Such a heat seal may be formed by arranging the layers, before applying heat to at least a portion of one or more of the layers to form the heat seal. In some embodiments, the heat-seal comprises a heat-sealed region across substantially the entire internal faces of the first gel separator layer and second gel separator layer. In other words, substantially the entire internal face of the first gel separator layer is heat-sealed to the adjacent layers which contact the internal face of the first gel separator layer (solid solvent-cast electrode layer, and optionally also the second gel separator layer when the edges of the second gel separator layer extend beyond the solid solvent-cast electrode layer). Similarly, substantially the entire internal face of the second gel separator layer may be heat-sealed to the adjacent layers which contact the internal face of the second gel separator layer (solid solvent-cast electrode layer, and optionally also the first gel separator layer when the edges of the first gel separator layer extend beyond the solid solvent-cast electrode layer).

[0105] This heat-sealed region across substantially the entire internal faces may be referred to as “face lamination” of the layers concerned. Face lamination has the benefit that the layers are very securely adhered to one another, and therefore are much less likely to move relative to one another during use of a cell containing the stack, providing a cell with increased safety. Face lamination also protects from possible detrimental effects of the shrinking of layers which may occur during assembly or use of the cell, which again could lead to a short-circuit and cell failure.

[0106] In some embodiments, the first gel separator layer and second gel separator layer each extend beyond a peripheral edge of the solid solvent-cast electrode layer such that they contact one another beyond the peripheral edge of the first electrode layer; and the first gel separator layer and second gel separator layer are adhered to one another by a heat-seal at a point where the first gel separator layer and second gel separator layer contact one another. In other words, the first gel separator layer and second gel separator layer are heat-sealed to one another at a peripheral location. In some embodiments, the solid solvent-cast electrode layer is not adhered to either of the first gel separator layer or second gel separator layer.

[0107] Such peripheral heat-sealing may be referred to as “edge lamination”, and provides active adhesion between the first gel separator layer and second gel separator layer, without adhering them to the intermediate solid solvent-cast electrode layer. This provides the benefit of allowing liquid electrolyte (“filling electrolyte”) to be more easily introduced to the solid solvent-cast electrode layer after assembly of the stack, while still providing improved adhesion between the layers to minimise the risk of relative movement of the layers.

[0108] Edge lamination may be achieved in a similar way to face lamination, by applying heat to the layers to be adhered together, except that the heat is applied in the discrete location(s) at the periphery of the stack where edge lamination is desired, rather than across the entire face of the layer. Electrochemical secondary cell

[0109] A second aspect of the invention provides an electrochemical secondary cell comprising a stack according to the first aspect.

[0110] In some embodiments, the electrochemical secondary cell is a lithium ion secondary cell.

[0111] In some embodiments, the electrochemical secondary cell further comprises a second gel electrode layer in contact with the second gel separator layer.

[0112] Electrochemical energy storage device

[0113] A third aspect of the invention is an electrochemical energy storage device comprising an electrochemical cell according to the second aspect.

[0114] Method of manufacturing a stack

[0115] A fourth aspect of the invention is a method of manufacturing the stack according to the first aspect, the method comprising: positioning a solid solvent-cast electrode layer between a first gel separator layer and a second gel separator layer; and placing a gel electrode layer into contact with the first gel separator layer.

[0116] As described above, there may be no “active” adhesion between layers, instead relying on the “passive” adhesion provided by the tackiness of the gelled layers.

[0117] In some embodiments, the method comprises applying heat across the entire area of the first gel separator layer and the second gel separator layer to form a heat seal across the internal faces of the first gel separator layer and second gel separator layer. This achieves the “face lamination” described above.

[0118] In some embodiments, the method comprises positioning the solid solvent-cast electrode layer (e.g. anode layer) between the first gel separator layer and the second gel separator layer; placing the gel electrode layer (e.g. gel cathode layer) into contact with the first gel separator layer, and passing the resulting structure through a heater assembly. In some embodiments, the heater assembly comprises one or more of heated belts and rollers. In some embodiments, the heater assembly comprises one or more heated belts to apply heat to the structure, and one or more rollers to apply pressure to the structure, thereby adhering the layers within the structure to one another across the entire area of the layer surfaces which contact one another. In some embodiments, the method comprises stacking a plurality of the resultant structures on top of one another to reach a desired number of layers, before terminating with a further assembly of a solid solvent-cast electrode layer (e.g. anode layer) between a first gel separator layer and a second gel separator layer.

[0119] In some embodiments, the method comprises heat-sealing portions of the respective first and second gel separator layers which extend beyond a peripheral edge of the solid solvent-cast electrode layer, thereby forming a heat-seal between the first gel separator layer and the second gel separator layer.

[0120] In some embodiments, the method comprises exposing the stack to a liquid electrolyte to allow the liquid electrolyte to soak into the space between the two gel separator layers surrounding the solid solvent-cast electrode layer. In some embodiments, this exposure to liquid electrolyte is performed after forming the heat-seal between the first gel separator layer and the second gel separator layer.

[0121] In some embodiments, exposing the stack to the liquid electrolyte comprises submerging the stack in the liquid electrolyte for a predetermined period of time.

[0122] In some embodiments, exposing the stack to the liquid electrolyte comprises submerging the stack in the liquid electrolyte for at least an hour, for example at least 2 hours, at least 3 hours, at least 5 hours, at least 10 hours, at least 12 hours, or for about 12 hours. In some embodiments, exposing the stack to the liquid electrolyte comprises submerging the stack in the liquid electrolyte for 1 to 15 hours, for example 2 to 15 hours, 3 to 15 hours, 5 to 15 hours, 10 to 15 hours or 10 to 12 hours.

[0123] In some embodiments, exposing the stack to the liquid electrolyte comprises assembling the stack with other components to form a complete cell, filling the cell with the liquid electrolyte and then vacuum-sealing the cell.

[0124] Brief Description of the Drawings

[0125] Figure 1 is a schematic cross section through a stack according to the invention.

[0126] Figure 2 is a schematic cross section through a plurality of stacks according to the invention, assembled together to form the basis of an electrochemical battery.

[0127] Figure 3 shows the first cycle discharge capacity during formation of a pouch cell incorporating a stack of the invention and a comparative pouch cell. Figure 4 shows the first cycle efficiency of a pouch cell incorporating a stack of the invention and a comparative pouch cell.

[0128] Figure 5 shows the discharge capacity retention after 3 cycles for a pouch cell incorporating a stack of the invention and a comparative pouch cell.

[0129] Detailed description

[0130] A stack 1 according to the invention is shown schematically in Figure 1, and an assembly 2 of a plurality of stacks is shown schematically in Figure 2.

[0131] The stack 1 is made up of first gel cathode layer 11, second gel cathode layer 12, aluminium foil current collector layer 13, first solvent-cast anode layer 14, second solvent-cast anode layer 15, copper foil current collector layer 16, first gel separator layer 17 and second gel separator layer 18.

[0132] The aluminium foil current collector layer 13 carries on each side a primer layer of conductive carbon (not shown), which is deposited onto the aluminium foil by preparing a slurry of conductive carbon, casting onto the aluminium foil before drying to form the primer layer.

[0133] The first gel cathode layer 11 is adhered to a first side of the aluminium foil current collector layer 13, and the second gel cathode layer 12 is adhered to a second side of the aluminium foil current collector layer 13. The primer layer (not shown) lies as an interlayer between the aluminium foil surface and the gel cathode layer on each side of the aluminium foil current collector layer 13. The adhesion between each gel cathode layer and the primed aluminium foil is achieved by extruding the gel cathode layers 11 and 12 onto the primed aluminium foil current collector layer 13 and relying on the natural adhesion of the gelled layers to the current collector layer. However, additional heat and / or pressure may be applied to strengthen the adhesion in some cases.

[0134] The first solvent-cast anode layer 14 is adhered to a first side of the copper foil current collector layer 16, and the second solvent-cast anode layer 15 is adhered to a second side of the copper foil current collector layer 16. This sandwich arrangement of the three layers is achieved by tandem casting two identical aqueous slurries containing the solid components of the solvent-cast anode layers onto the first and second sides of the copper foil current collector layer 16 and drying to remove the water and solidify the solvent-cast anode layers.

[0135] Surrounding the entire periphery of the first and second solvent-cast anode layers 14, 15 is an envelope formed by the first gel separator layer 17 and the second gel separator layer 18. The first gel separator layer 17 and second gel separator layer 18 are adhered to one another by a heat-seal across their entire internal faces, which seals the first gel separator layer 17 and second gel separator layer 18 to one another around their peripheral, overlapping edge, and also to the first and second solvent-cast anode layers 14, 15 which lie between them.

[0136] The second gel cathode layer 12 is in contact with the face of the first gel separator layer 17 which is opposite to the inner face of the first gel separator layer 17, which contacts the second solvent-cast anode layer 15. In a similar way to the heat-seal formed between the first gel separator layer 17 and second gel separator layer 18, a heat-seal is formed between the second gel cathode layer 12 and the first gel separator layer 17 by applying sufficient heat to the layers until a seal is formed.

[0137] The stack includes layers sufficient to form the basis of a full electrochemical cell, since the second solvent-cast anode layer 15 and second gel cathode layer 12, each supported on a current collector foil layer, lie on either side of the first gel separator layer 17. This electrode-separator-electrode structure will allow the stack to function as a full electrochemical cell when assembled with other necessary components within a suitable housing and connected to a source of electrical energy.

[0138] Figure 2 shows an extended stack 2, containing three units of the stack 1 shown in Figure 1, along with a further anode sub-unit to terminate the stack at the top. This extended stack 2 forms the basis of a battery of cells which can be used to reversibly store electrochemical energy. The result of assembling the stacks together is a plurality of cells, each separated by current collector layers and each containing an anode and a cathode, separated by a gel separator.

[0139] Examples

[0140] Example 1

[0141] An anode slurry composition was prepared comprising graphite, silicon oxide, conductive carbon additive and polyacrylic acid binder, dispersed in water. The slurry was tandem-coated onto both sides of a copper foil current collector to 66 g / m2, to a density of 1.6 g / m3. This created an anode sandwich structure.

[0142] Gel separators were prepared by mixing PVDF-HFP, ethylene carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, LiFSI and LiTDI, before extruding sandwiched between two 50 pm-thick mylar sheets to form a film structure. The thickness of each gel separator film between the mylar sheets was 20 pm.

[0143] Gel cathodes were prepared by a method which included first mixing bulk powdered components with electrolyte in a ‘premix’ stage. The premix slurry was then batch-injected into a twin-screw extruder. Granules were then produced and allowed to freefall from the end of the twin screw. The granules were then sandwiched between copper foil and a release fdm and hot-rolled down to target thickness to form the gel cathode.

[0144] The gel cathode had the following composition:

[0145] Electrolyte 1 had the following composition:

[0146] Two gel cathode sheets prepared in this way were placed on either side of a primed aluminium foil current collector to create a cathode sandwich structure. The priming of the current collector consisted of a layer of conductive carbon on each side of the aluminium foil, onto which the cathode sheet was placed.

[0147] The cathode sandwich structure was cut to the desired size for incorporation into the stack.

[0148] The anode sandwich structure prepared as above was punched using a die cutter to produce an individual piece. The piece punched out in this way was larger than the cathode pieces in such a way that when the cathode is placed on the anode, a border of anode 1 mm wide extends beyond the edge of the cathode.

[0149] Gel separator pieces between mylar sheets were cut from the fdm manufactured as described above using a punch and swing arm press. An electrode stack was then made by removing one of the two supporting mylar sheets from each separator, placing one piece of separator behind and one piece of separator on top of the cathode, ensuring that the separator edges were aligned with one another, sandwiching the cathode sandwich structure between them with an equal border of separator material surrounding the edges of the cathode sandwich structure.

[0150] This assembly, with a supporting mylar sheet remaining on each face, was then heat-sealed across the entire faces of the gel separator layers, using a sealer (Audionvac VMS 163), with seal settings -0.4 bar, 1 second, temperature recorded to be 80 °C using a thermocouple.

[0151] The anode sandwich structure was then placed into contact with an exposed surface of one of the gel separator layers after removing the mylar sheets.

[0152] To build a multilayer cell, this process was repeated, placing heat-sealed stacks against one another, until the desired number of cathode layers are achieved, finishing with an anode on top. An aluminium tab was welded onto the cathode foil current collector using a Branson L20 Ultrasonic welder, such that it protruded from between the separator layers. A nickel tab was welded to the anode foil current collectors using a Branson L20 Ultrasonic welder, such that it also protruded from between the separator layers.

[0153] The electrode stack was then sealed within pouch bag material using a sealer (Star Universal Platen Heater). Uiquid electrolyte was then added to the stack in the pouch using a pipette before vacuum sealing (Audionvac VMS 163).

[0154] Cells were then clamped in a jig between two pieces of foam over each side of the cell (Rogers Corp, BISCO HT-840) and compressed to 100 kPa. Cells were placed into a temperature-controlled oven (Binder KMF 115) set at 30 °C and connected to a potentiostat (VMP3e). Cells were soaked for 12 hours to allow liquid electrolyte to wet into the stack, PEIS was recorded every hour to monitor wetting of electrolyte (10 mV amplitude, frequency range from 500 kHz to 0. 1 Hz, with 10 points per decade).

[0155] Cells were formed using the same equipment and temperature as the soaking step.

[0156] Comparative Example 1

[0157] A cell equivalent to that of Example 1, except that it contained gel anode layers in place of the solvent-cast anode layers, was prepared. The gel anode layers were made in an analogous way to the gel cathodes made in Example 1. The gel anode composition was as follows, and it was ensured that it was formulated to correspond with the solvent-cast anode composition used in Example 1 :

[0158] Electrochemical testing

[0159] Cells were charged for 1 hr at C / 20, then at C / 10 up to 4.2 V, then a CV hold was used until the current reached C / 40. Cells were discharged to 2.5 V at C / 5. This process was repeated an additional two times, however the charging step was conducted at C / 10 in the two repeat steps.

[0160] Rate testing was conducted on cells at 30 °C on VMP3e. Test conditions C / 5, D / 5, C / 3, ID, C / 3, 2D, C / 3, 5D, C / 3, 7D, C / 3, 10D. CV hold at 4.2 V until current decay was C / 40. Operating voltage between 4.2 V and 2.5 V.

[0161] Figure 3 shows the first cycle discharge capacity during formation of the pouch cells of Example 1 and Comparative Example 1. The first cycle discharge capacity is significantly higher for the cell of Example 1.

[0162] Figure 4 shows the first cycle efficiency (FCE) of the pouch cells of Example 1 and Comparative Example 1. The FCE is significantly higher for the cell of Example 1.

[0163] Figure 5 shows the discharge capacity retention after 3 cycles for the pouch cells of Example 1 and Comparative Example 1. The capacity retention is significantly higher for the cell of Example 1.

Claims

Claims1. A stack for an electrochemical cell, having a laminate structure comprising: a first gel separator layer and a second gel separator layer; a solid solvent-cast electrode layer between the first and second gel separator layers; and a gel electrode layer in contact with the first gel separator layer.

2. The stack according to claim 1, wherein the solid solvent-cast electrode layer is a solid solvent-cast anode layer.

3. The stack according to claim 1 or 2, wherein the gel electrode layer is a gel cathode layer.

4. The stack according to any one of the preceding claims, wherein the solid solvent-cast electrode layer comprises an electrochemically active material layer deposited on a foil current collector layer.

5. The stack according to claim 4, wherein the foil current collector layer comprises aluminium, copper or carbon fibre.

6. The stack according to any one of the preceding claims, wherein the first gel separator layer and second gel separator layer each extend beyond the peripheral edge of the solid solvent-cast electrode layer around the entire peripheral edge of the solid solvent-cast electrode layer.

7. The stack according to any one of the preceding claims, wherein the first gel separator layer and second gel separator layer are adhered to one another by a heat-sealed border region which extends around the periphery of the solid solvent-cast electrode layer.

8. The stack according to any one of claims 1 to 6, wherein the first gel separator layer and second gel separator layer are adhered to one another and to the solid solvent-cast electrode layer by a heat seal across the internal faces of the first gel separator layer and second gel separator layer.

9. The stack according to any one of the preceding claims, wherein the solid solvent-cast electrode layer is impregnated with free liquid electrolyte.

10. The stack according to claim 9, wherein the free liquid electrolyte comprises a linear or cyclic carbonate liquid electrolyte and one or more lithium salts.

11. The stack according to any one of the preceding claims, wherein the gel electrode layer comprises one or more polymers independently selected from poly(ethyleneglycol dimethacrylate), poly(ethyleneglycol diacrylate), poly(propyleneglycol dimethacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (PU), poly(vinylidene difluoride) (PVdF), poly(vinylidene fhioride-co-hexafluoropropylene) (PvDF-HFP), poly(ethylene oxide) (PEO), poly-L-lactic acid (PLA), polystyrene (PS), poly(ethyleneglycol dimethylether), poly(ethyleneglycol diethylether), poly[bis(methoxy ethoxyethoxide)-phosphazene], poly(dimethylsiloxane) (PDMS), polyacene, polydisulfide, polystyrene, polystyrene sulfonate, polypyrrole, polyaniline, polythiophene, polythione, polyvinyl pyridine (PVP), polyvinyl chloride (PVC), polyaniline, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiafulvalene-substituted polystyrene, ferrocene-substituted polyethylene, carbazole-substituted polyethylene, polyoxyphenazine, poly (heteroacene), poly[(4- styrenesulfonyl)(trifluoromethanesulfonyl)imide-co-methoxy-polyethyleneglycolacrylate] (Li[PSTFSI-co-MPEGA]), sulfonated poly(phenylene oxide) (PPO), N,N-dimethylacryl amide (DMAAm), lithium 2 -acrylamido-2 -methyl- 1 -propane sulfonate (LiAMPS), Poly(lithium 2- Acrylamido-2 -Methylpropane sulfonic Acid-Co-Vinyl Triethoxysilane), polyethyleneoxide(PEO) / poly(lithium sorbate), PEO / poly(lithium muconate), PEO / [poly(lithium sorbate)+BF3], PEO copolymer, PEO terpolymer, and NIPPON SHOKUBAI® polymer.

12. The stack according to claim 11 wherein the gel electrode layer further comprises a linear or cyclic carbonate liquid electrolyte, one or more lithium salts and an electrochemically active material.

13. The stack according to any one of the preceding claims, wherein the first and second gel separator layers each independently comprise one or more polymers independently selected from poly(ethyleneglycol dimethacrylate), poly(ethyleneglycol diacrylate), poly(propyleneglycol dimethacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (PU), poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP), polyethylene oxide) (PEO), poly-L-lactic acid (PLA), polystyrene (PS), poly(ethyleneglycol dimethylether), poly(ethyleneglycol diethylether), poly[bis(methoxy ethoxyethoxide)-phosphazene], poly(dimethylsiloxane) (PDMS), polyacene, polydisulfide, polystyrene, polystyrene sulfonate, polypyrrole, polyaniline, polythiophene, polythione, polyvinyl pyridine (PVP), polyvinyl chloride (PVC), polyaniline, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(p-phenylene), poly(triphenylene), polyazulene, polyfluorene, polynaphthalene, polyanthracene, polyfuran, polycarbazole, tetrathiafulvalene-substituted polystyrene, ferrocenesubstituted polyethylene, carbazole-substituted polyethylene, poly oxyphenazine, poly(heteroacene), poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide-co-methoxy-polyethyleneglycolacrylate](Li[PSTFSI-co-MPEGA]), sulfonated poly(phenylene oxide) (PPO), N,N-dimethylacryl amide (DMAAm), lithium 2 -acrylamido-2 -methyl- 1 -propane sulfonate (LiAMPS), Poly(lithium 2- Acrylamido-2 -Methylpropane sulfonic Acid-Co-Vinyl Triethoxysilane), polyethyleneoxide(PEO) / poly(lithium sorbate), PEO / poly(lithium muconate), PEO / [poly(lithium sorbate)+BF3], PEO copolymer, PEO terpolymer, and NIPPON SHOKUBAI® polymer.

14. The stack according to any one of the preceding claims, wherein the first and second gel separator layers and the gel electrode layer each independently comprise one or more polymers independently selected from poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co- hexafluoropropylene) (PvDF-HFP), poly(methyl methacrylate) (PMMA), polyethylene oxide) (PEO), poly-L-lactic acid (PLA) and polystyrene (PS).

15. The separator-electrode-separator stack according to claim 13 or 14, wherein the first and second gel separator layers further comprise a linear or cyclic carbonate liquid electrolyte and one or more lithium salts.

16. The stack according to any one of the preceding claims, wherein the first and second gel separator layers each independently have a thickness of from 10 to 30 pm.

17. An electrochemical secondary cell comprising a stack according to any one of claims 1 to 16.

18. The electrochemical secondary cell according to claim 17, further comprising a second gel electrode layer in contact with the second gel separator layer.

19. An electrochemical cell according to claim 17 or 18, which is a lithium-ion electrochemical secondary cell.

20. An electrochemical energy storage device comprising an electrochemical cell according to any one of claims 17 to 19.

21. A method of manufacturing the stack according to any one of claims 1 to 16 comprising: positioning a solid solvent-cast electrode layer between a first gel separator layer and a second gel separator layer; and placing a gel electrode layer into contact with the first gel separator layer.

22. The method according to claim 21, comprising applying heat across the entire area of the first gel separator layer and the second gel separator layer to form a heat seal across the internal faces of the first gel separator layer and second gel separator layer.

23. The method according to claim 21, comprising heat-sealing portions of the respective first and second gel separator layers which extend beyond a peripheral edge of the solid solvent-cast electrode layer, thereby forming a heat-seal between the first gel separator layer and the second gel separator layer.

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