WO2024157101A1

WO2024157101A1 - Electrochemical secondary cell

Info

Publication number: WO2024157101A1
Application number: PCT/IB2024/050235
Authority: WO
Inventors: Alex MADSEN; Daniel MORDAK
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2023-01-27
Filing date: 2024-01-10
Publication date: 2024-08-02
Anticipated expiration: 2025-07-27
Also published as: GB202301183D0; GB2626576A

Abstract

An electrochemical secondary cell is described including a cathode, an anode and a porous separator between the cathode and the anode. The anode comprises a polymer-electrolyte gel matrix phase and a dispersed phase comprising a negative active material. The electrochemical secondary cell may find use in electrochemical energy storage devices.

Description

ELECTROCHEMICAL SECONDARY CELL

Field of the Invention

The present invention relates to an electrochemical secondary cell comprising a cathode, an anode and a separator, and energy storage devices containing such cells.

Background of the Invention

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.

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.

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.

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 A1, which attempts to manufacture electrochemical devices free of liquid electrolytes.

Gel electrodes are assembled together with other gel or solid-state components to form a solid-state cell, thereby reducing the risk of fire due to the removal of free liquid from the cell. The cell manufacturing costs are also reduced because the gel components can be produced by simpler processing steps without the need for slow drying of solvent needed for solvent cast electrodes. However this comes at the expense of ionic conductivity, with solid- state cells having reduced rate capabilities due to the absence of the highly ionically conducting liquid electrolyte.

There is a need for electrochemical cells which not only offer improved safety benefit but also retain high ionic conductivities leading to high rate capability.

Summary of the Invention

The invention relates generally to an electrochemical secondary cell comprising a cathode, an anode and a separator, and in particular to an electrochemical secondary cell comprising a cathode, an anode and a porous separator wherein the porous separator is impregnated with a liquid electrolyte salt solution.

A first aspect of the invention is an electrochemical secondary cell comprising: a cathode comprising a first polymer-electrolyte gel matrix phase and a dispersed phase comprising a positive active material; an anode comprising a second polymer-electrolyte gel matrix phase and a dispersed phase comprising a negative active material; and a solid porous separator between the cathode and the anode; wherein the solid porous separator is impregnated with a liquid electrolyte salt solution.

The electrochemical secondary cell of the first aspect contains a gel cathode and a gel anode. Each electrode 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 cell of increased safety. However the cell also contains a solid porous separator between the cathode and the anode, the solid porous separator being impregnated with a liquid electrolyte salt solution. In this way, the cell provides improved safety over traditional secondary cells due to the use of gel electrodes while demonstrating ionic conductivity superior to all-solid-state cells due to the presence of the liquid electrolyte salt solution.

The cell of the invention therefore achieves a compromise between operational safety and ionic conductivity.

A second aspect of the invention provides an electrochemical secondary cell comprising: a cathode; an anode comprising a polymer-electrolyte gel matrix phase and a dispersed phase comprising a negative active material; and a porous separator between the cathode and the anode.

The use of a gel anode in the cell of the second aspect provides safety benefits due to the reduced flammability of the cell and also provides cost benefits relative to a cell containing a solvent-cast anode.

It has been found that adding liquid electrolyte salt solution to the gel anode of the cell decreases the tortuosity of the anode, increases the effective ionic conductivity of the anode and thereby improves the rate capability of the cell. Without wishing to be bound by theory, it is believed that residual porosity within the anode is at least partially filled by the liquid electrolyte salt solution, reducing the tortuosity of the anode and increasing its effective ionic conductivity.

Thus 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 separator, thereby providing ionic conductivity across the separator between the two 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(s). In this way, the electrolyte within the polymer-electrolyte gel matrix phase may be tailored for the gelation and functioning of the gel anode while the free electrolyte within the cell can may be tailored for ionic conductivity, 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(s). In this way manufacture of the cell is simplified with a single electrolyte composition used throughout.

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. Cathode

The cathode of the first aspect comprises a first polymer-electrolyte gel matrix phase; and a dispersed phase comprising a positive active material. In other words, the cathode of the first aspect is a gel cathode.

In some embodiments, the cathode of the second aspect is a solvent-cast cathode. In some embodiments, the cathode of the second aspect is a solvent-cast cathode comprising a positive active material, a binder and a conductive additive.

In some embodiments, the dispersed phase of the cathode of the first aspect makes up from 80 to 90 wt% of the cathode, for example from 82 to 88 wt%, from 85 to 88 wt% or from 85 to 86 wt%.

In some embodiments, the positive active material makes up at least 50 vol% of the cathode of the first aspect, 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%.

In some embodiments the positive active material makes up from 50 to 75 vol% of the cathode of the first aspect, 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%.

In some embodiments the positive active material makes up from 62 to 75 vol% of the cathode of the first aspect, 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 cathode of the first aspect comprises from 55 to 90 wt% of the positive active material, based on the total cathode weight, for example from 60 to 90 wt%, from 70 to 90 wt%, from 75 to 90 wt%, from 80 to 90 wt%, from 82 to 88 wt%, or from 84 to 86 wt%.ln some embodiments, the positive active material makes up at least 50 vol% of the cathode of the second aspect, 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%.

In some embodiments the cathode of the second aspect comprises from 55 to 99 wt% positive active material, based on the total cathode weight, for example from 60 to 99 wt%, from 70 to 99 wt%, from 80 to 99 wt%, from 90 to 99 wt%, or from 95 to 98 wt%. The volumetric median particle size (D50) of the positive active material used in the cathode of the first or second aspect may be from 0.5 to 50 pm, for example from 1 to 40 pm, from 2 to 30 pm, from 5 to 25 pm or from 5 to 20 pm.

D50 is the volumetric median particle size. In other words, it represents the particle size in microns which splits the volume distribution of a population of particles in half, with 50 vol% of the particles having a particle size below that value and 50 vol% having a particle size above that value.

The skilled person will appreciate that the volume median particle size D50 can be measured using a Malvern Mastersizer 3000 using the light scattering method set out in ASTM B822- 20, applying the Mie scattering theory.

In some embodiments the cathode of the first or second aspect comprises a first conductive additive.

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

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

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

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

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

In some embodiments, the first conductive additive is present in an amount of from 0.5 wt% to 2.5 wt%, based on the total weight of the cathode of the first or second aspect. 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 cathode of the first or second aspect, 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%.

In some embodiments, the dispersed phase of the cathode of the first aspect comprises from 2 vol% to 4 vol% positive active material, based on the total volume of the dispersed phase of the cathode, 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%.

In some embodiments, the dispersed phase of the cathode of the first aspect comprises from 96 vol% to 98 vol% positive active material, based on the total volume of the dispersed phase of the cathode, 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%.

In some embodiments the dispersed phase of the cathode of the first aspect 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 cathode of the first aspect 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.

In some embodiments the dispersed phase of the cathode of the first aspect 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%.

In some embodiments, the dispersed phase of the cathode of the first aspect consists of the positive active material and the first conductive additive.

In some embodiments, the first polymer-electrolyte gel matrix phase of the first aspect comprises a mixture of a gelling polymer and a liquid electrolyte. In some embodiments, the first polymer-electrolyte gel matrix phase of the first aspect 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 first polymer-electrolyte gel matrix phase consists of the gelling polymer and the liquid electrolyte.

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

In some embodiments, the cathode of the first aspect 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%.

In some embodiments, the first polymer-electrolyte gel matrix phase of the first aspect 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%.

In some embodiments the first 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 first polymer-electrolyte gel matrix phase of the first aspect 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%.

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

In some embodiments, the cathode of the first aspect comprises the electrolyte in an amount of from 20 to 35 vol%, based on the total volume of the cathode, for example from 21 to 34 vol%, from 22 to 33 vol%, from 23 to 32 vol% or from 24 to 31 vol%. In some embodiments, the cathode of the first aspect comprises the electrolyte in an amount of from 10 to 15 wt%, based on the total weight of the cathode, for example from 11 to 15 wt%, from 11 to 14 wt%, or from 11 to 13 wt%.

In some embodiments, the first polymer-electrolyte gel matrix phase of the first aspect 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%.

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

The identity of the electrochemically active materials in the cell of the first or second aspect is not of particular importance. The benefits of the invention based on the presence of free liquid electrolyte in the cell 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.

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. 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.

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.

The cathode of the first aspect may further comprise a binder. The cathode of the second aspect may further comprise a binder.

In some embodiments the binder comprises one or more polymers. In some embodiments, the binder comprises one or more polymers selected from those listed above as options for the gelling polymer. In some embodiments, the binder comprises a cellulosic polymer, for example carboxymethylcellulose (CMC).

It is noted that a polymer which functions as a binder when used in a solvent-cast (solid) electrode may form a gel when exposed to the electrolyte within a gel electrode, such that the same polymer may function as a binder within a solvent-cast electrode and a gelling polymer within a gel electrode. For example, PvDF may be used as a binder within a solid, solvent-cast electrode, but may be used as a gelling polymer when used in a gel electrode.

In some embodiments, the cathode of the first or second aspect is an extruded cathode. In other embodiments, the cathode is a hot-rolled cathode. In other embodiments, the cathode is prepared by extruding an electrode precursor composition through a die to form a film.

In some embodiments the cathode of the first or second aspect is formed by one or more hot-rolling steps carried out on an electrode precursor composition, followed by one or more extrusion steps.

In some embodiments the cathode of the first or second aspect has a thickness 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 cathode 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.

In some embodiments the cathode of the first or second aspect 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, and comprises the positive active material in an amount of from 50 to 75 vol% of the cathode, for example from 55 to 70 vol%, from 60 to 69 vol%, from 62 to 68 vol% or from 64 to 69 vol%.

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

In some cases, the extruded cathode 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 the anode (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.

As an alternative to the above, the cathode of the second aspect may be a solid, solventcast cathode.

In some embodiments, the cathode of the second aspect is a solid cathode comprising particulate positive active material, optionally a conductive additive, and optionally a binder.

In some embodiments, the cathode of the second aspect is a solid cathode comprising particulate positive active material, a conductive additive, and a binder.

The solid, solvent-cast cathode may comprise a positive active material and a conductive additive. Further optional additives may be present including one or more binders.

The conductive additive in the solid, solvent-cast cathode may be a conductive additive as discussed above for the first conductive additive. The positive active material in the solid, solvent-cast cathode may also be as discussed above. For example, the positive active material 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).

The solid, solvent-cast cathode 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.

Anode

The anode of the first and second aspects each comprise a polymer-electrolyte gel matrix phase; and a dispersed phase comprising a negative active material. In other words, the anodes of the first and second aspects are each gel anodes.

In some embodiments, the negative active material makes up at least 50 vol% of the anode of the first or second aspect, 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%.

In some embodiments the negative active material makes up from 50 to 75 vol% of the anode of the first or second aspect, 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%.

In some embodiments the negative active material makes up from 62 to 75 vol% of the anode of the first or second aspect, 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 anode of the first or second aspect comprises from 65 to 85 wt% of the negative active material, based on the total anode weight, for example from 70 to 80 wt% or from 75 to 78 wt%.

The volumetric median particle size (D50) of the negative active material may be from 0.5 to 50 pm, for example from 1 to 40 pm, from 2 to 30 pm, from 5 to 25 pm or from 5 to 20 pm. In some embodiments the dispersed phase of the anode of the first or second aspect further comprises a second conductive additive.

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

In some embodiments the second conductive additive of the first or second aspect comprises or consists of one or more of carbon black and graphite.

Examples of commercially available carbon black include Ketjen Black and Super C65. Super C65 has a BET surface area of 62 m²/g and a primary particle size less than 50 nm.

In some embodiments the second conductive additive comprises carbon nanotubes, for example single wall carbon nanotubes or multiwall carbon nanotubes. Single wall carbon nanotubes are available from OCSiAl and may have an aspect ratio of 3000:1.

In some embodiments, the second conductive additive of the first or second aspect is present in an amount of from 0.5 wt% to 2.5 wt%, based on the total weight of the anode, for example from 0.5 to 2.0 wt%, from 0.5 to 1.5 wt% or from 0.8 to 1.2 wt%.

In some embodiments, the second conductive additive of the first or second aspect is present in an amount of from 1.5 vol% to 2.5 vol%, based on the total weight of the anode, 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%.

In some embodiments, the dispersed phase of the anode of the first or second aspect comprises from 2 vol% to 4 vol% conductive additive, based on the total volume of the dispersed phase of the anode, 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%.

In some embodiments, the dispersed phase of the anode of the first or second aspect comprises from 1 wt% to 3 wt% conductive additive, based on the total weight of the dispersed phase of the anode, for example from 1 wt% to 2 wt%, from 1 wt% to 1.6 wt%, from 1.1 vol% to 1.5 wt% or from 1.2 wt% to 1.4 wt%. In some embodiments, the dispersed phase of the anode of the first or second aspect comprises from 96 vol% to 98 vol% negative active material, based on the total volume of the dispersed phase of the anode, 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%.

In some embodiments, the dispersed phase of the anode of the first or second aspect comprises from 96 wt% to 99 wt% negative active material, based on the total weight of the dispersed phase of the anode, for example from 97 wt% to 99 wt%, from 98 wt% to 99 wt%, from 98.2 wt% to 99.0 wt%, from 98.4 vol% to 99.0 vol% or from 98.5 wt% to 98.9 wt%.

The dispersed phase of the anode of the first or second aspect may consist of the negative active material and the conductive additive. In some embodiments the dispersed phase consists of the negative active material and a conductive additive comprising carbon black. In some embodiments the dispersed phase consists of the negative active material and carbon black.

In some embodiments, the dispersed phase of the anode of the first or second aspect makes up from 70 to 80 wt% of the anode, based on the total anode weight, for example from 75 to 80 wt% or from 76 to 78 wt%.

In some embodiments, the polymer-electrolyte gel matrix phase of the anode of the first or second aspect makes up from 20 to 30 wt% of the anode, based on the total anode weight, for example from 20 to 25 wt% or from 22 to 24 wt%.

In some embodiments, the polymer-electrolyte gel matrix phase of the first or second aspect comprises a mixture of a gelling polymer and a liquid electrolyte, wherein the weight ratio of electrolyte: polymer is from 2 to 6, for example from 3 to 4 or from 3.5 to 4.0. In some embodiments, the second polymer-electrolyte gel matrix phase consists of the gelling polymer and the liquid electrolyte.

In some embodiments, the anode of the first or second aspect comprises a gelling polymer in an amount of from 5 to 10 vol%, based on the total volume of anode, for example from 5 to 9 vol%, from 5 to 8 vol%, from 5.5 to 8 vol% or from 6 to 8 vol%.

In some embodiments, the second polymer-electrolyte gel matrix phase of the first or second aspect 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%.

In some embodiments, the second polymer-electrolyte gel matrix phase of the first or second aspect comprises 18 to 28 wt% gelling polymer, based on the total weight of second polymer-electrolyte gel matrix phase, for example from 20 to 25 wt%.

In some embodiments, the second polymer-electrolyte gel matrix phase of the first or second aspect 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%.

In some embodiments, the second polymer-electrolyte gel matrix phase of the first or second aspect comprises the electrolyte in an amount of from 75 to 85 wt%, based on the total weight of polymer-electrolyte gel matrix phase, for example from 75 to 84 wt%, from 76 to 86 wt%, from 77 to 84 wt%, from 77 to 83 wt%, from 78 to 83 wt%, from 78 to 82 wt%, from 79 to 82 wt%, from 79 to 81 wt%, or about 80 wt%.

In some embodiments, the anode of the first or second aspect comprises the electrolyte in an amount of from 10 to 25 wt%, based on the total weight of the anode, for example from 10 to 20 wt%, from 12 to 20 wt%, from 14 to 20 wt%, from 16 to 20 wt%, from 17 to 20 wt%, from 17 to 19 wt% or about 18 wt%.

In some embodiments, the anode of the first or second aspect comprises the electrolyte in an amount of from 20 to 35 vol%, based on the total volume of the anode, for example from 21 to 34 vol%, from 22 to 33 vol%, from 23 to 32 vol% or from 24 to 31 vol%.

In some embodiments, the second polymer-electrolyte gel matrix phase of the first or second aspect makes up from 20 vol% to 50 vol% of the anode, 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%.

In some embodiments, the anode of the first or second aspect comprises 2 to 10 wt% gelling polymer, based on the total weight of the anode, for example from 2 to 8 wt%, from 3 to 7 wt%, from 4 to 6 wt% or from 4 to 5 wt%. The identity of the electrochemically active materials in the cell of the first or second aspect is not of particular importance. The benefits of the invention based on the presence of free liquid electrolyte in the cell 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.

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.

The anode of the first aspect may further comprise a binder. The anode of the second aspect may further comprise a binder.

In some embodiments, the anode of the first or second aspect is an extruded anode. In other embodiments, the anode is a hot-rolled anode. In other embodiments, the anode is prepared by extruding an electrode precursor composition through a die to form a film.

In some embodiments the anode of the first or second aspect is formed by one or more hot- rolling steps carried out on an electrode precursor composition, followed by one or more extrusion steps.

In some embodiments the anode of the first or second aspect has a thickness 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 anode 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.

In some embodiments the anode of the first or second aspect 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, and comprises the negative active material in an amount of from 62 to 75 vol% of the anode, 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 anode of the first or second aspect has a porosity of less than about 5% by volume. In some cases, the porosity of the anode is less than 5 vol%, less than 3 vol% or less than 2 vol%. To phrase in another manner, the volumetric density of the anode may be at least 95%, suitably at least about 97% or 98% of the density of a perfectly non-porous anode.

In some cases, the extruded anode may for 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 the cathode (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.

Polymer-electrolyte gel matrix phases within electrodes

The cathode and anode of the first aspect cell comprise first and second polymer-electrolyte gel matrix phases respectively. The anode of the second aspect cell also comprises a polymer-electrolyte gel matrix phase.

The polymer-electrolyte gel matrix phases of the first or second aspect each comprise a gel matrix formed by the swelling of a swellable polymer when the polymer absorbs a liquid electrolyte. The polymer-electrolyte gel matrix phase therefore comprises a gel comprising a polymer and absorbed liquid electrolyte. The dispersed phase may be distributed through the bulk of the polymer-electrolyte gel matrix phase, forming the electrode.

In some embodiments, the polymer-electrolyte gel matrix phases each comprise one or more gelling polymers independently selected from poly(ethyleneglycol dimethacrylate), poly(ethyleneglycol diacrylate), poly(propyleneglycol dimethacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (Pll), 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, 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-Methylpropanesulfonic Acid-Co- Vinyl T riethoxysilane), polyethyleneoxide(PEO)/poly(lithium sorbate), PEO/poly(lithium muconate), PEO/[poly(lithium sorbate)+BFs], PEO copolymer, PEO terpolymer, and NIPPON SHOKUBAI® polymer.

In some embodiments, the polymer-electrolyte gel matrix phases each comprise PMMA.

The polymer-electrolyte gel matrix phases may each comprise one or more gelling polymers selected from the above list and a liquid electrolyte.

In some embodiments, the liquid electrolyte comprises or consists of a solvent comprising one or more cyclic or linear carbonate compounds. In some embodiments the solvent comprises one or more cyclic carbonate compounds. In some embodiments the solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl-methyl carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and y-butyrolactone.

In some embodiments the solvent comprises or consists of a mixture of at least two different cyclic carbonate compounds. In some embodiments the solvent comprises or consists of a mixture of at least three different cyclic carbonate compounds. In some embodiments the solvent comprises or consists of a mixture of at least four different cyclic carbonate compounds.

In some embodiments the solvent comprises or consists of a mixture of ethylene carbonate (EC) and propylene carbonate (PC), optionally comprising one or more further cyclic carbonate compounds. In some embodiments the solvent comprises or consists of a mixture of ethylene carbonate (EC) and propylene carbonate (PC), optionally comprising one or more further cyclic carbonate compounds selected from vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

In some embodiments the solvent comprises or consists of a mixture of ethylene carbonate (EC) and propylene carbonate (PC), further comprising one or more further cyclic carbonate compounds, wherein the total amount of EC and PC in the solvent is at least 50 wt%, for example at least 60 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt% or at least 90 wt%. In some embodiments the solvent comprises or consists of a mixture of EC, PC, VC and FEC.

In some embodiments the solvent comprises EC in an amount of from 65 to 75 wt%, based on the total solvent weight, for example from 68 to 72 wt%. In some embodiments the solvent comprises PC in an amount of from 20 to 30 wt%, based on the total solvent weight, for example from 20 to 25 wt%. In some embodiments the solvent comprises FEC in an amount of from 1 to 5 wt%, based on the total solvent weight, for example from 2 to 4 wt%. In some embodiments the solvent comprises VC in an amount of from 3 to 8 wt%, based on the total solvent weight, for example from 5 to 7 wt%. In some embodiments the solvent consists of 68 to 72 wt% EC, from 20 to 25 wt% PC, from 2 to 4 wt% FEC and from 5 to 7 wt% VC.

Such solvent compositions within the electrolyte of the polymer-electrolyte gel matrix phase demonstrate a good balance of gelling properties and electrochemical stability.

In some embodiments, the liquid electrolyte further comprises a lithium salt. Examples of suitable lithium salts include LiPFe, UBF4, 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.

In some embodiments, the liquid electrolyte comprises from 10 to 20 wt% lithium salt(s), for example from 12 to 18 wt% or from 15 to 17 wt%, based on the total liquid electrolyte weight. Separator

The electrochemical cell of the first aspect comprises a solid porous separator between the cathode and the anode. The separator may be a film disposed between the cathode and the anode. In some embodiments the separator may contact the cathode on one side and the anode on the other side. The separator is solid, i.e. not a gel or semi-solid. Furthermore, the separator is porous, meaning that the separator provides a path for the conduction of ions between the anode and the cathode when the separator is impregnated with a liquid electrolyte. In some embodiments the separator is liquid-permeable, allowing the permeation of liquid between the cathode and the anode such that ionic conductivity between the cathode and the anode is facilitated.

The separator may comprise one or more polymers.

In some embodiments, the separator comprises non-woven material.

In some embodiments, the non-woven material comprises polymer fibres and/or glass fibres.

In some embodiments, the non-woven material comprises a polyolefin. In some embodiments, the non-woven material comprises one or more of polyethylene, polypropylene and aramid.

The separator within the cell of the second aspect is a porous separator. The separator may be a solid porous separator as described above for the first aspect and all of the options and preferences set out under the first aspect above for the separator apply equally to the separator of the second aspect.

Alternatively, the separator within the cell of the second aspect may be a non-solid porous separator, for example a semi-solid separator or a gel separator.

Free liquid electrolyte salt solution

The cell of the first or second aspect may contain a liquid electrolyte salt solution which impregnates the separator between the cathode and the anode. This may also be denoted a “filling electrolyte” or “free electrolyte” to distinguish from the liquid electrolyte which is already present within the polymer-electrolyte gel matrix phase of any gel electrodes within the cell. In some embodiments the cell therefore contains two electrodes and free liquid electrolyte between the electrodes, thereby providing high ionic conductivity between the electrodes through the free liquid electrolyte and improving the rate capability of the cell. The free electrolyte may be added to the cell after assembly of the electrodes and separator, before the cell is sealed, as explained in more detail below.

The liquid electrolyte salt solution may be introduced to the cell after cell assembly by drawing the electrolyte into the cell under vacuum followed by sealing the cell.

In some embodiments, the liquid electrolyte salt solution comprises a lithium salt dissolved in a solvent.

In some embodiments, the free electrolyte permeates the free space around and between the components of the cell, including the electrodes and the separator, thereby providing ionic conductivity across the separator between the two 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. In this way, the electrolyte within the polymer-electrolyte gel matrix phase can have a composition tailored for the gelation and functioning of the gel electrode while the free electrolyte within the cell can have a composition tailored for ionic conductivity, the filling of free space within the cell and the reduction of tortuosity.

In some embodiments, the free electrolyte comprises or consists of a solvent comprising one or more cyclic or linear carbonate compounds. In some embodiments the solvent comprises one or more cyclic carbonate compounds. In some embodiments the solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl-methyl carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and y-butyrolactone.

In some embodiments the solvent within the free electrolyte comprises or consists of a mixture of at least two different cyclic carbonate compounds. In some embodiments the solvent comprises or consists of a mixture of at least three different cyclic carbonate compounds. In some embodiments the solvent comprises or consists of a mixture of at least four different cyclic carbonate compounds.

In some embodiments the solvent within the free electrolyte comprises or consists of a mixture of ethylene carbonate (EC) and propylene carbonate (PC), optionally comprising one or more further cyclic carbonate compounds. In some embodiments the solvent within the free electrolyte comprises or consists of a mixture of ethylene carbonate (EC) and propylene carbonate (PC), optionally comprising one or more further cyclic carbonate compounds selected from vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

In some embodiments the solvent within the free electrolyte comprises or consists of dimethyl carbonate (DMC), optionally comprising one or more further cyclic carbonate compounds. In some embodiments the solvent within the free electrolyte comprises or consists of dimethyl carbonate (DMC), optionally comprising one or more further cyclic carbonate compounds selected from vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

In some embodiments the solvent within the free electrolyte comprises or consists of a mixture of ethylene carbonate (EC) and propylene carbonate (PC), further comprising one or more further cyclic carbonate compounds, wherein the total amount of EC and PC in the solvent is at least 50 wt%, for example at least 60 wt%, at least 70 wt% or at least 75 wt%. In some embodiments the solvent within the free electrolyte comprises or consists of a mixture of EC, PC, VC and FEC.

In some embodiments the solvent within the free electrolyte comprises or consists of DMC, further comprising one or more further cyclic carbonate compounds, wherein the total amount of DMC in the solvent is at least 50 wt%, for example at least 60 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt% or at least 90 wt%. In some embodiments the solvent within the free electrolyte comprises or consists of a mixture of DMC, VC and FEC.

In some embodiments the solvent within the free electrolyte comprises EC in an amount of from 65 to 75 wt%, based on the total solvent weight, for example from 68 to 72 wt%. In some embodiments the solvent within the free electrolyte comprises PC in an amount of from 20 to 30 wt%, based on the total solvent weight, for example from 20 to 25 wt%. In some embodiments the solvent within the free electrolyte comprises FEC in an amount of from 1 to 5 wt%, based on the total solvent weight, for example from 2 to 4 wt%. In some embodiments the solvent within the free electrolyte comprises VC in an amount of from 3 to 8 wt%, based on the total solvent weight, for example from 5 to 7 wt%. In some embodiments the solvent within the free electrolyte consists of 68 to 72 wt% EC, from 20 to 25 wt% PC, from 2 to 4 wt% FEC and from 5 to 7 wt% VC.

In some embodiments the solvent within the free electrolyte comprises DMC in an amount of from 85 to 95 wt%, based on the total solvent weight, for example from 90 to 95 wt%. In some embodiments the solvent within the free electrolyte comprises FEC in an amount of from 1 to 5 wt%, based on the total solvent weight, for example from 2 to 4 wt%. In some embodiments the solvent within the free electrolyte comprises VC in an amount of from 3 to 8 wt%, based on the total solvent weight, for example from 5 to 7 wt%. In some embodiments the solvent within the free electrolyte consists of 90 to 95 wt% DMC, 2 to 4 wt% FEC and 5 to 7 wt% VC.

Such solvent compositions within the free electrolyte demonstrate good electrochemical stability and ability to wet into the components of the cell after assembly.

In some embodiments, the free electrolyte further comprises a lithium salt. Examples of suitable lithium salts include LiPF₆, 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 free electrolyte comprises a mixture of two or more different lithium salts.

In some embodiments, the free electrolyte comprises from 10 to 40 wt% lithium salt(s), for example from 12 to 40 wt% or from 12 to 38 wt%, based on the total liquid electrolyte weight.

In some embodiments, the free electrolyte comprises from 10 to 20 wt% lithium salt(s), for example from 12 to 18 wt% or from 15 to 17 wt%, based on the total liquid electrolyte weight.

In some embodiments, the free electrolyte comprises from 30 to 40 wt% lithium salt(s), for example from 32 to 38 wt% or from 34 to 36 wt%, based on the total liquid electrolyte weight.

In some embodiments, the concentration of the lithium salt in the solvent is from 1.5 to 2.3 mol L’¹.

The cell may be an alkali metal ion secondary cell, for example a sodium-ion secondary cell or a lithium-ion secondary cell. Preferably the cell is a lithium-ion secondary cell. In some embodiments the electrochemical secondary cell comprises the cathode laminated with a current collector, for example a metallic foil, and the anode laminated with a current collector, for example a metallic foil.

A third aspect of the invention is a method of producing an electrochemical cell according to the first aspect comprising: mixing a first gelling polymer, a positive active material, a first electrolyte component and optionally a first conductive additive and processing the mixture to form a cathode; mixing a second gelling polymer, a negative active material, a second electrolyte component and optionally a second conductive additive and processing the mixture to form an anode; positioning the cathode on a first current collector and the anode on a second current collector; disposing a solid porous separator between the cathode and the anode; and impregnating the solid porous separator with a liquid electrolyte salt solution.

All of the compositional options and preferences set out above for the first aspect apply equally to the method of the second aspect, including the identities and the relative amounts of the various components of the cell.

In some embodiments, the processing comprises thermal processing.

In some embodiments, the processing comprises hot rolling. In some embodiments, the processing comprises extrusion.

In some embodiments the thermal processing comprises passing an electrode precursor composition through a roller assembly at a temperature of at least 50 °C, for example at least 60 °C, at least 70 °C, at least 80 °C, at least 90 °C or at least 100 °C. In some embodiments the thermal processing comprises passing the electrode precursor composition through rollers at a temperature of up to 150 °C, for example up to 140 °C or up to 130 °C. In some embodiments the thermal processing comprises passing the electrode precursor composition through rollers at a temperature of from 50 °C to 150 °C, for example from 60 °C to 150 °C, from 70 °C to 150 °C, from 80 °C to 150 °C, from 80 °C to 140 °C, from 90 °C to 140 °C, from 100 °C to 140 °C or from 110 °C to 130 °C.

The roller assembly may comprise two rollers separated by a small distance such that the electrode is pressed into a thin film when passed through the rollers.

In some embodiments the thermal processing comprises extruding the electrode. In some embodiments the thermal processing comprises extruding the electrode using an extrusion apparatus comprising one or more screw feeding sections and an extrusion die. In some embodiments, the temperature of the die is at least 50 °C, for example at least 60 °C, at least 70 °C, at least 80 °C, at least 90 °C or at least 100 °C. In some embodiments the temperature of the die is up to 150 °C, for example up to 140 °C or up to 130 °C. In some embodiments the temperature of the die is from 50 °C to 150 °C, for example from 60 °C to 150 °C, from 70 °C to 150 °C, from 80 °C to 150 °C, from 80 °C to 140 °C, from 90 °C to 140 °C, from 100 °C to 140 °C or from 110 °C to 130 °C.

In some embodiments impregnating the solid porous separator with a liquid electrolyte salt solution comprises stacking the electrodes and separator together to form a cell before injecting electrolyte into the cell under vacuum and sealing the cell.

A fourth aspect of the invention is a method of producing an electrochemical cell according to the second aspect comprising: providing a cathode; mixing a polymer, a negative active material, an electrolyte component and optionally a conductive additive and extruding the mixture to form a gelled anode comprising pores; positioning the cathode on a first current collector and the anode on a second current collector; placing a porous separator between the cathode and the anode; and adding a liquid electrolyte salt solution to the anode such that the pores of the anode are at least partially impregnated with a liquid electrolyte salt solution.

In some embodiments the liquid electrolyte salt solution is added to the anode by vacuum filling or by dropping liquid onto the anode.

In some embodiments, electrodes and the separator are combined by z-stacking or wrapping whereby electrodes are placed alternately between separator layers. After such assembly, cells may be electrically connected by welding tabs to current collector foils within the cell. The cell may then be packaged into a pouch and filled with the liquid electrolyte salt solution, for example by vacuum filling as described above.

In some embodiments, after addition of the liquid electrolyte salt solution to the assembled cell, the cell is left for 12-24 hours at a temperature of 25-35 °C, for example at about 30 °C, to allow the liquid electrolyte salt solution to fully wet into the cell structure.

A fifth aspect of the invention provides an electrochemical energy storage device comprising an electrochemical secondary cell according to the first aspect or the second aspect. In some embodiments, the electrochemical energy storage device is a battery. In some embodiments, the electrochemical energy storage device is a lithium-ion battery. The electrochemical energy storage device may provide improved safety due to reduced fire risk and higher rate capability making the electrochemical energy storage device suitable for high power applications.

Brief Description of the Drawings

Figure 1 is a plot comparing the discharge capacities of two comparative cells (dotted lines) and one cell according to the first aspect of the invention (solid line), at different discharge rates between 0.2C and 10C.

Figure 2 is a plot comparing the discharge capacities of a comparative cell (dotted line) and a cell according to the second aspect of the invention (solid line), at different discharge rates between 0.2C and 10C.

Examples

Example 1

Three different cells were prepared. Comparative Cell A contained extruded gel electrodes along with a gel separator. Comparative Cell B contained solvent cast electrodes and a porous separator and was filled with liquid electrolyte. Cell 1 contained extruded gel electrodes and a porous polyolefin separator and was filled with liquid electrolyte.

The gel electrodes are made by a method which includes 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 film and hot-rolled down to target thickness to form the gel electrode.

The three cells were Swagelok cells. In all cases, the anode was placed into the Swagelok cell casing, then a small amount of electrolyte was added to the anode surface. The separator was then added to the anode. A further small amount of electrolyte was then added to the separator surface before the cathode was added to the top. A “filling electrolyte” was then added down the edge onto the exposed separator surface, before the cell was sealed shut. Cells were then placed in a temperature-controlled oven at 30 °C and left for 12 hours to allow the liquid electrolyte to soak into the components. Cells were then formed by 3 initial cycles at C/10, D/10 at 30 °C. Then the cells were rate tested with charge rate of C/5 and the subsequent discharges of C/5, C/3, C/2, 1 C, 2C, 3C, 5C, 7C and 10 C at both 30 °C and 45 °C. The operating voltage range was 4.2 V - 2.5 V. There was a CV hold at the end of the charge cycle at 4.2V until the current dropped to C/40.

The compositions of the cathode, anode and filling electrolyte used in Cell 1 are provided in the tables below:

Table 1 - Cell 1 cathode composition

Table 2 - Cell 1 anode composition

Table 3 - Filling electrolyte added to Cell 1 after assembly

Table 4 - Electrolyte 1 composition (contained within electrodes)

Figure 1 shows the measured discharge capacities of Cell 1 according to the first aspect invention alongside Comparative Cell A and Comparative Cell B.

Comparative Cell A, containing extruded gel electrodes along with a gel separator, has a low discharge capacity at rates above 1 C, and a particularly low capacity at 10C, indicating poor rate capability and a lack of suitability for high power applications such as electric vehicle batteries.

By contrast, Cell 1 has a discharge capacity at 10C which is notably higher and comparable with a traditional cell (Comparative Cell B) containing solvent cast electrodes and a porous separator and filled with liquid electrolyte. Cell 1 therefore provides equivalent rate capability to a traditional cell, along with improved safety due to the use of gel electrodes and the resultant reduction in the amount of free liquid electrolyte contained within the cell.

The data in Figure 1 show that cells according to the invention offer improved safety without compromising on rate capability.

Example 2

Two cells were prepared, a comparative cell (Comparative Cell C) containing solvent-cast anode and cathode with a porous glass fibre separator between them, impregnated with electrolyte, and an inventive cell (Cell 2) containing a solvent-cast cathode and a gel anode, with a porous glass fibre separator between them, impregnated with electrolyte. The two cells were Swagelok cells. In all cases, the anode was placed into the Swagelok cell casing, then a small amount of electrolyte was added to the anode surface. The separator was then added to the anode. A further small amount of electrolyte was then added to the separator surface before the cathode was added to the top. The rest of the electrolyte required was then added down the edge onto the exposed separator surface, before the cell was sealed shut. Cells were then placed in a temperature-controlled oven at 30 °C and left for 12 hours to allow the liquid electrolyte to soak into the components. Cells were then formed by 3 initial cycles at C/10, D/10 at 30 °C. Then the cells were rate tested with charge rate of C/5 and the subsequent discharges of C/5, C/3, C/2, 1 C, 2C, 3C, 5C, 7C and 10 C at both 30 °C and 45 °C. The operating voltage range was 4.2 V - 2.5 V. There was a CV hold at the end of the charge cycle at 4.2V until the current dropped to C/40.

The solvent cast electrodes were made by dispersing components in a planetary mixer before casting onto a drawdown coater. Coatings were dried on a hotplate before being dried in a vacuum oven for 12 hours at 120 °C.

The gel anode was made by first mixing bulk powders 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 film and hot-rolled down to target thickness to form the electrode.

Table 5 - Cell 2 cathode composition

Table 6 - Cell 2 anode composition

Table 7 - Filling electrolyte added to Cell 2 after assembly

Properties of the gel anode were assessed before and after the impregnation with a liquid electrolyte salt solution. These are set out in Table 8 below.

Table 8

The results in Table 8 show that the addition of liquid electrolyte salt solution to the anode increased the effective electrode conductivity, reduced the ionic resistance and reduced the tortuosity. Firstly, ionic resistance of the electrodes was found by symmetrical cells and measured by EIS. Tortuosity was then determined by the following equation:

T = Rlon Z\K£/2d

Figure 2 shows the measured energy densities of Cell 2 according to the second aspect invention (solid line) alongside Comparative Cell C (dotted line).

The results show that the energy densities of the two cells are comparable within experimental error at all discharge rates tested between 0.2C and 10C.

Claims

1. An electrochemical secondary cell comprising: a cathode; an anode comprising a polymer-electrolyte gel matrix phase and a dispersed phase comprising a negative active material; and a porous separator between the cathode and the anode.

2. An electrochemical cell according to claim 1, further comprising free electrolyte which permeates free space around and between the cathode, anode and separator.

3. An electrochemical cell according to claim 1 or 2, wherein the dispersed phase of the anode further comprises a conductive additive.

4. An electrochemical cell according to any one of the preceding claims, wherein the negative active material is selected from one or more of graphite, silicon and silicon oxide.

5. An electrochemical cell according to any one of the preceding claims, wherein the porous separator is a solid porous separator.

6. An electrochemical cell according to any one of the preceding claims, wherein the porous separator comprises non-woven material.

7. An electrochemical cell according to claim 6, wherein the non-woven material comprises polymer fibres and/or glass fibres.

8. An electrochemical cell according to claim 7, wherein the non-woven material comprises one or more of polyethylene, polypropylene and aramid.

9. An electrochemical cell according to any one of the preceding claims, wherein the liquid electrolyte salt solution comprises a lithium salt dissolved in a solvent.

10. An electrochemical cell according to claim 9, wherein the solvent comprises one or more cyclic or linear carbonate compounds.

11. An electrochemical cell according to claim 9, wherein the solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl-methyl carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate and y-butyrolactone.

12. An electrochemical cell according to any one of claims 9 to 11 , wherein the lithium salt comprises one or more of LiPF₆, Li BF₄, 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.

13. An electrochemical cell according to any one of claims 9 to 12, wherein the concentration of the lithium salt in the solvent is from 1.5 to 2.3 mol L’¹.

14. An electrochemical cell according to any one of the preceding claims, wherein the anode comprises from 50 to 75 wt% of the negative active material, based on the total anode weight.

15. An electrochemical cell according to any one of the preceding claims, wherein the anode comprises from 20 to 30 wt% of the polymer-electrolyte gel matrix phase, based on the total anode weight.

16. An electrochemical cell according to any one of the preceding claims, wherein the polymer-electrolyte gel matrix phase comprises 15 to 25 wt% gelling polymer, based on the total weight of polymer-electrolyte gel matrix phase.

17. An electrochemical cell according to any one of the preceding claims, wherein the polymer-electrolyte gel matrix phase comprises one or more gelling polymers selected from poly(ethyleneglycol dimethacrylate), poly(ethyleneglycol diacrylate), poly(propyleneglycol di methacrylate), poly(propyleneglycol diacrylate), poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), polyurethane (Pll), poly(vinylidene difluoride) (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PvDF-HFP), poly(ethylene oxide) (PEO), 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, 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-Methylpropanesulfonic Acid-Co- Vinyl T riethoxysilane), polyethyleneoxide(PEO)/poly(lithium sorbate), PEO/poly(lithium muconate), PEO/[poly(lithium sorbate)+BF₃], PEO copolymer, PEO terpolymer, and NIPPON SHOKUBAI® polymer.

18. An electrochemical cell according to any one of the preceding claims, wherein the cathode is a solid cathode comprising particulate positive active material, optionally a conductive additive, and optionally a binder.

19. An electrochemical cell according to any one of the preceding claims, which is a lithium-ion secondary electrochemical cell.

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

21. A method of producing an electrochemical cell according to any one of claims 1 to 19 comprising: providing a cathode; mixing a polymer, a negative active material, an electrolyte component and optionally a conductive additive and extruding the mixture to form a gelled anode comprising pores; positioning the cathode on a first current collector and the anode on a second current collector; placing a porous separator between the cathode and the anode; and adding a liquid electrolyte salt solution to the anode such that the pores of the anode are at least partially impregnated with a liquid electrolyte salt solution.

22. A method according to claim 21 , wherein the liquid electrolyte salt solution is added to the anode by vacuum filling or by dropping liquid onto the anode.