Electrode formulations

Abstract

The present invention provides an electrode formulation comprising a) about 70 wt% to about 90 wt% of a cathode active material; b) about 0.1 wt% to about 5 wt% graphene or graphene derivative; c) about 1 wt% to about 20 wt% of a binder; and d) about 0 wt% to about 10 wt% of a carbon additive other than graphene or a graphene derivative; wherein the cathode active material and graphene or graphene derivative form a composite material comprising particles of the cathode active material each coated with the graphene or graphene derivative. The present invention further provides a slurry comprising the electrode formulation, a cathode electrode comprising the electrode formulation, a battery comprising the cathode electrode, a kit of parts comprising the electrode formulation, and methods of preparing the electrode formulation and cathode electrode disclosed herein.

Description

[0001] ELECTRODE FORMULATIONS

[0002] Field of Invention

[0003] The present invention provides an electrode formulation, an electrode and a battery comprising the electrode formulation. The present invention also provides methods of preparing the electrode formulation, an electrode comprising the electrode formulation, and a battery comprising such an electrode.

[0004] The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

[0005] Alkali metal-ion batteries (AMIBs) such as lithium-ion batteries are important battery technologies. Much effort has been focused on improving the performance of batteries, for example by seeking to improve the performance of lithium ion-based cathodes. Due to the continual demand of batteries for newer and more advanced electronic devices, there remains a need to further improve the performance of batteries.

[0006] Summary of Invention

[0007] The present invention provides an electrode formulation comprising: a) about 70 wt% to about 90 wt% of a cathode active material; b) about 0.1 wt% to about 5 wt% graphene or graphene derivative; c) about 1 wt% to about 20 wt% of a binder; and d) about 0 wt% to about 10 wt% of a carbon additive other than graphene or a graphene derivative; wherein the cathode active material and graphene or graphene derivative form a composite material comprising particles of the cathode active material each partially or substantially coated with the graphene or graphene derivative.

[0008] The present inventors have found that the electrode formulation of the present invention enables the preparation of a cathode for AMIBs that displays especially stable and improved electrochemical performance, such as improved electrical conductivity, efficiency, and capacity retention compared to a commercial AMIBs. In particular, the present inventors have shown that a lithium ion pouch cell and lithium ion coin cell using a cathode comprising the electrode formulation of the invention display superior performance to corresponding batteries that do not use the cathode formulation of the present invention.

[0009] The present invention also provides a slurry comprising the electrode formulation of the present invention and an organic solvent. The present invention further provides a cathode electrode comprising the electrode formulation of the present invention, a battery assembly comprising such an electrode, and a kit of parts comprising the cathode formulation of the present invention together with a support (e.g. an aluminium foil), or a cathode electrode of the present invention, an anode electrode; an electrolyte; and a separator.

[0010] The present invention also provides a method of preparing an electrode formulation of the present invention, said method comprising the steps of: i. mixing a cathode active material with graphene or a graphene derivative to form a powder comprising the cathode active material and graphene; ii. dispersing the powder in a first solvent to form a colloidal solution; iii. removing the first solvent from the colloidal solution to provide a composite material comprising particles of the cathode active material each coated with graphene or the graphene derivative; and iv. mixing the composite material with a binder to provide an electrode formulation of the present invention.

[0011] Further aspects and embodiments of the invention will be discussed by reference to the following numbered clauses.

[0012] 1 . An electrode formulation comprising: a) about 70 wt% to about 90 wt% of a cathode active material; b) about 0.1 wt% to about 5 wt% graphene; c) about 1 wt% to about 20 wt% of a binder; and d) about 0 wt% to about 10 wt% of a carbon additive other than graphene or a graphene derivative; wherein the cathode active material and graphene are present in the form of a composite material comprising particles of the cathode active material each partially or substantially coated with graphene. 2. The electrode formulation of clause 1 , wherein the cathode active material is selected from the group consisting of LixFePC , LixNiCOMnO2, LixCo02, LixNiO0.33Co0.33AI0.33O2, LixMn2O4, and LixNio.5Mn1.5O4, for example the cathode active material may be LiFePO4.

[0013] 3. The electrode formulation of any preceding clause, wherein the binder is polyvinylidene fluoride (PVDF).

[0014] 4. The electrode formulation of any preceding clause comprising about 75 wt% to about 85 wt% of the cathode active material, for example about 80 wt% of the cathode active material.

[0015] 5. The electrode formulation of any preceding clause comprising about 0.5 wt% to about 2 wt% graphene, for example about 1 wt% graphene.

[0016] 6. The electrode formulation of any preceding clause comprising about 5 wt% to about 20 wt% of the binder, for example about 15 wt% of the binder.

[0017] 7. The electrode formulation of any preceding clause comprising about 0 wt% to about 5 wt% of a carbon additive other than graphene or a graphene derivative, for example about

[0018] 4 wt%.

[0019] 8. The electrode formulation of any preceding clause, wherein the carbon additive other than graphene or a graphene derivative is carbon black.

[0020] 9. The electrode formulation of any preceding clause comprising about 75 wt% to about 95 wt% of the composite material.

[0021] 10. The electrode formulation of any preceding clause, wherein the cathode active material and graphene are present in the composite material at a weight ratio of about 70:1 to about 90:1 , for example about 80:1 .

[0022] 1 1. A slurry comprising the electrode formulation of any preceding clause and an organic solvent. 12. The slurry of clause 11 , wherein the slurry has a viscosity of about 5,000 mPa.s to about 7,000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1.5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

[0023] 13. The slurry of clause 11 or 12, wherein the organic solvent is N-methyl-2-pyrrolidone (NMP).

[0024] 14. A cathode electrode comprising a support coated with the electrode formulation of any one of clauses 1 to 10 or the slurry of any one of clauses 11 to 13.

[0025] 15. The cathode electrode of clause 14, wherein the support comprises aluminium, for example the support is an aluminium foil.

[0026] 16. The cathode electrode of clause 14 or 15 having a thickness of about 2 pm to about 20 pm, for example about 5 pm to about 7 pm.

[0027] 17. A battery comprising the cathode electrode of any one of clauses 14 to 16.

[0028] 18. The battery of clause 17, wherein the battery is a lithium ion battery, for example a lithium ion full cell battery.

[0029] 19. The battery of clause 17 or 18, wherein the battery is a pouch cell.

[0030] 20. A kit of parts comprising: a cathode formulation according to any one of clauses 1 to 10, or the slurry of any one of clauses 11 to 13, together with a support (e.g. an aluminium foil); or cathode electrode according to any one of clauses 14 to 16; an anode electrode; an electrolyte; and a separator.

[0031] 21. A method of preparing the electrode formulation of any one of clauses 1 to 10, wherein the method comprises: i. mixing a cathode active material with graphene or a graphene derivative to form a powder comprising the cathode active material and graphene; ii. dispersing the powder in a first solvent to form a colloidal solution; iii. removing the first solvent from the colloidal solution to provide a composite material comprising particles of the cathode active material each coated with graphene or the graphene derivative; and iv. mixing the composite material with a binder to provide the electrode formulation.

[0032] 22. The method according to clause 21 , wherein step i) comprises mixing the cathode active material with graphene or a graphene derivative and a carbon additive other than graphene or the graphene derivative to form the powder.

[0033] 23. The method according to clause 21 or 22, wherein step iv) comprises mixing the composite material with a binder and a carbon additive other the graphene or graphene.

[0034] 24. The method according to any one of clauses 21 to 23, wherein step ii) comprises sonicating the colloidal solution.

[0035] 25. The method according to any one of clauses 21 to 24, wherein the colloidal solution is sonicated at a frequency of at least 20 kHz.

[0036] 26. The method according to any one of clauses 21 to 25, wherein the first solvent is a polar protic solvent, for example ethanol.

[0037] 27. The method according to any one of clauses 21 to 26, wherein the method further comprises a step of suspending the electrode formulation provided after step iv) in a second solvent to form a slurry.

[0038] 28. The method according to clause 27, wherein the slurry has a viscosity of about 5,000 to about 7,000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

[0039] 29. The method according to clause 27 or 28, wherein the second solvent is NMP.

[0040] 30. A method of preparing a cathode electrode, the method comprising coating a support with the slurry of any one of clauses 1 1 to 13, followed by removing substantially all of the organic solvent from the slurry to provide the cathode electrode. 31. The method according to clause 30, wherein the support is coated with the slurry followed by heating the support at a temperature of about 50 °C to about 100 °C for about 1 hour to about 24 hours.

[0041] of the

[0042] FIG. 1 is a flowchart for the preparation of a cathode electrode formulation and subsequent preparation of the cathode electrode according to an example of the present invention.

[0043] FIG. 2 is a schematic diagram of the LFP / G cathode according to an example of the present invention. The width for the main coating area was fixed at 152±1 .0 mm. The right side of the coating area was left blank at 18.0 mm width. The left side of the coating was reserved for tab welding (23.0 mm) with 3.0 mm gap from the coating area.

[0044] FIG. 3 is a schematic diagram of the pouch battery according to an example of the present invention.

[0045] FIG. 4 includes (a) photographs of the cut cathode, anode, PTFE separator and the aluminium laminated pouch casing, (b) another schematic diagram showing the dimensions of the pouch battery and (c) photograph of the assembled pouch battery.

[0046] FIG. 5 shows a charge-discharge capacity curve of the 3.2V 10Ah LFP-G pouch cell during 100 cycles of cyclic charge-discharge.

[0047] FIG. 6 shows a selection of FE-SEM images showing the morphologies of the LFP / G composite at (a) X50k magnification (b) LFP / G composite electrode at X100k magnification, and (c) morphology of graphene structures used in this work..

[0048] FIG. 7 shows a Raman spectrum of the graphene in the LFP / G composite electrode.

[0049] FIG. 8 shows a conductivity vs concentration of graphene in LFP / G cathode formulation graph.

[0050] FIG. 9 is a flowchart of an alternative preparation method for the cathode electrode formulation and subsequent preparation of the cathode electrode.

[0051] Detailed Description

[0052] The present invention provides an electrode formulation comprising: a) about 70 wt% to about 90 wt% of a cathode active material; b) about 0.1 wt% to about 5 wt% graphene or graphene derivative; c) about 1 wt% to about 20 wt% of a binder; and d) about 0 wt% to about 10 wt% of a carbon additive other than graphene or a graphene derivative; wherein the cathode active material and graphene or graphene derivative form a composite material comprising particles of the cathode active material each coated with the graphene or graphene derivative.

[0053] As used herein, the word “comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components / features listed are intended to be present (e.g. the word “comprising” may be replaced by the phrases “consists of” or “consists essentially of”). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of’ or the phrase “consists essentially of” or synonyms thereof and vice versa.

[0054] As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a carbon capture moiety” includes two or more such carbon capture moieties. The term “plurality” as used herein means two or more. For example, the textile substrate of the carbon capture composite material may be coated or impregnated with at least 2 carbon capture moieties, for example 2 to 10,000, or more, carbon capture moieties.

[0055] The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, within 1 %, within 0.5%, within 0.1%, within 0.05%, within 0.01 %, within 0.005%, or within 0.001% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0056] The term “wt%” as used herein refers to the percentage mass of a particular substance in the electrode formulation with respect to the total mass of the electrode formulation, unless indicated otherwise. For example, an electrode formulation of the invention containing 70 wt% of a cathode active material is to be understood as containing 70 g of the cathode active material in every 100 g of the electrode formulation. For the avoidance of doubt, when the wt% of the components of the electrode formulation of the invention are provided herein, the values refer to the dry mass of the each component with respect to the total dry mass of the electrode formulation. That is to say that the wt% values for each component of the electrode formulation provided herein do not take into account any liquid carrier or solvent that maybe present, unless otherwise stated.

[0057] The electrode formulation of the present invention comprises from about 70 wt% to about 90 wt% of a cathode active material. For example, from about 75 wt% to about 85 wt% of a cathode active material. In certain embodiment, the electrode formulation comprises about 80 wt% of a cathode active material.

[0058] The cathode active material may be a lithium-containing or sodium-containing active material. Examples of sodium-containing active material include, but are not limited to, NaFePC and NaCoC>2. Typically, the cathode active material is a lithium-containing material. For example, a lithium-containing complex phosphate having the general formula LiMPC , wherein M is one or more of Fe(ll), Mn(ll), Co(ll), and Ni(ll))). Examples of lithium- containing complex phosphate include, but are not limited to, LiFePC , LiNiPC , LiCoPC , LiMnPC , LiFeaNibPO4, LiFeaC0bPO4, LiFe VInbPC , LiNiaC0bPO4, LiNiaMnbPO4 (a+b^ 1 , 0<a<1 , and 0<b<1 ), LiFecNidCoeP04, LiFecNidMnePO4, LiNicCodMneP04 (c+d+e^ 1 , 0<c<1 , 0<d< 1 , and 0<e<1 ), and LiFetNigCOhMniPC (f+g+h+i 1 , 0<f< 1 , 0<g< 1 , 0<h< 1 , and 0<i< 1 ). Further examples of cathode active material that may be used include LixNiCOMnO2, UXC0O2, LixNiO0.33Co0.33AI0.33O2, LixMn2O4, and LixNio.5Mn1.5O4 (0<x<1). In exemplary embodiments, the cathode active material is LiFePO4.

[0059] The cathode active material used in the preparation of the electrode formulation of the present invention typically has an average particle size (D50) of less than about 5 pm. For example, less than about 4 pm, less than about 3 pm, less than about 2 pm, or less than about 0.1 pm. Typically, the average particle size (D50) is from about 0.1 pm to about 2 pm (e.g. from about 1 pm to about 2 pm). When the cathode active material is LiFePC , the average particle size (D50) is typically from about 1 pm to about 2 pm.

[0060] As used herein, the term “average particle size (D50)” refers to the mean particle size of a material based on the volume-based particle size distribution, often measured by the laser diffraction or light scattering particle size distribution measurements. The cathode active material used in the preparation of the electrode formulation of the present invention typically also has a BET surface area greater than about 1 m2 / g, for example greater than about 10 m2 / g, or greater than about 50 m2 / g. For example, the BET specific surface area may be from about 1 m2 / g to about 100 m2 / g, from about 5 m2 / g to about 30 m2 / g, or from about 5 m2 / g to about 20 m2 / g (e.g. from about 5 m2 / g to about 15 m2 / g). When the cathode active material used in the preparation of the electrode formulation of the present invention is LiFePC , the BET surface area is typically from about 5 m2 / g to about 15 m2 / g.

[0061] The surface area of materials disclosed herein is determined from nitrogen adsorption data using the Brunauer-Emmett-Teller (BET) method. See J. Am. Chem. Soc. 1938, 60, 309- 331 , which is incorporated herein by reference.

[0062] Suitable graphene derivatives include, but are not limited to, graphene oxide and reduced graphene oxide. Typically, the electrode formulation comprises graphene.

[0063] Typically, the graphene is obtained from commercially available sources. However, it may also be formed by separation of graphene sheets (e.g., via exfoliation) from a graphite or carbon fiber material by, e.g., subjecting the graphite or carbon fiber material to acidic conditions (e.g., sulfuric or nitric acid), followed by shearing processes such as milling, sonication, etc.

[0064] The graphene used in the preparation of the electrode formulation of the present invention typically has an average particle size (D50) of less than about 100 pm. For example, less than about 50 pm or less than about 25 pm. The graphene typically also has a BET surface area of from about 100 m2 / g to about 800 m2 / g, for example from about 100 m2 / g to about 700 m2 / g, from about 100 m2 / g to about 600 m2 / g, or from about 200 m2 / g to about 600 m2 / g, or from about 100 m2 / g to about 500 m2 / g.

[0065] The electrode formulation of the present invention may comprise from about 0.5 wt% to about 2 wt% graphene. The present inventors have found that electrode formulations comprising about 1 wt% graphene are particularly effective at producing a cathode electrode that displays a stable electrochemical performance.

[0066] In the electrode formulation of the present invention, the cathode active material and graphene form a composite material comprising particles of the cathode active material, each particle partially or substantially coated with the graphene or graphene derivative. That is to say that the electrode formulation comprises a composite material comprising particles of the cathode active material each partially or substantially coated with the graphene or graphene derivative. Typically, the composite material makes up from about 75 wt% to about 95 wt% of the electrode formulation.

[0067] Typically, substantially all of the cathode active material and graphene or graphene derivative present in the electrode formulation is in the form of a composite material comprising particles of the cathode active material each partially or substantially coated with the graphene or graphene derivative. Typically, each particle of the cathode active material in the composite material is substantially coated with the graphene or graphene derivative.

[0068] The term "substantially" is used herein to indicate that the characteristic, property, or parameter that follows is realized or satisfied to a degree that does not adversely affect the intended result of the present invention. For example, when the particles of a cathode active material are substantially coated with graphene or graphene derivative, this means that the surface of the particles may be at least about 50%, at least about 60%, least about 70%, at least about 80%, least about 90%, or at least about 99%, or about 100%, coated with graphene or graphene derivative. When the particles of a cathode active material are partially coated with the graphene or graphene derivative, the surface of the particles may be less than about 50% coated, for example from about 1% to about 40% coated (e.g. from about 10% to about 40% coated).

[0069] The composite material comprising particles of the cathode active material each partially or substantially coated with the graphene or graphene derivative graphene typically has an average particle size (D50) of less than about 10 pm. For example, less than about 5 pm, less than about 1 pm, or less than about 0.5 pm. In certain embodiments, the composite material has an average particle size (D50) of from about 0.1 to about 0.3 pm. The composite material typically also has a BET surface area of from about 1 m2 / g to about 100 m2 / g, for example from about 1 m2 / g to about 50 m2 / g, from about 1 m2 / g to about 25 m2 / g, or from about 1 m2 / g to about 20 m2 / g (e.g. from about 5 m2 / g to about 20 m2 / g).

[0070] The composite material may comprise the cathode active material and graphene or graphene derivate at a mass ratio of from about 18:1 to about 800:1 . In certain embodiments, the composite material comprises the cathode active material and graphene or graphene derivate at a mass ratio of from about 70:1 to about 90:1 , for example about 80:1 .

[0071] The electrode formulation may comprise about 1 wt% to about 20 wt% of a binder, for example about 5 wt% to about 20 wt% (e.g. about 15 wt%) of a binder. Suitable binders include, but are not limited to, fluorinated polymers such as poly(vinyldifluoroethylene) (PVDF), poly(vinyldifluoroethylene-co-hexafluoropropylene) (PVDF-HFP), poly(tetrafluoroethylene) (PTFE), polyimides, poly(ethylene) oxide, polyvinyl-alcohol (PVA), cellulose, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, polyvinyl pyrrolidone (PVP), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene- butadiene rubber (SBR), and copolymers and mixtures thereof. Typically, the binder is a fluorinated polymers such as poly(vinyldifluoroethylene) (PVDF). In exemplary embodiments, the binder is polyvinylidene fluoride (PVDF).

[0072] The electrode formulation of the present invention comprises from about 0 wt% to about 10 wt% of a carbon additive other than graphene or a graphene derivative. For example, from about 0 wt% to about 5 wt% (e.g. about 4 wt%) of a carbon additive other than graphene or a graphene derivative. Suitable carbon additives other than graphene or a graphene derivative include, but are not limited to, amorphous carbon such as carbon black, graphite, coke, carbon fiber, carbon nanotubes, and mixtures thereof. Typically, the carbon additive is carbon black. Thus, in certain embodiments, the electrode formulation of the present invention comprises about 0 wt% to about 10 wt% carbon black. For example, about 0 wt% to about 5 wt% carbon black (e.g. about 4 wt%).

[0073] Preferably, the carbon additive has a surface area suitable for its use as a battery conductive additive. For example, when the carbon additive is carbon black, the carbon black may have a BET surface area of from about 30 m2 / g to about 90 m2 / g, for example from about 50 m2 / g to about 70 m2 / g, from about 55 m2 / g to about 65 m2 / g, or from about 60 m2 / g to about 65 m2 / g.

[0074] In certain embodiments, the electrode formulation of the invention may be used to prepare a slurry. The term “slurry” as used herein refers to a mixture of solids suspended in a liquid. When the electrode formulation is used to prepare a slurry, the slurry may comprise any suitable solvent or carrier liquid commonly used in the manufacture of electrodes comprising lithium-containing or sodium-containing active material. For example, the solvent or carrier may be selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dibutyl phthalate (DBP), triethyl phosphate (TEP), and mixtures thereof. Typically, the solvent or carrier is NMP. Accordingly, in certain aspects, the present invention provides a slurry comprising the electrode formulation of the invention and a suitable solvent or carrier liquid. A slurry of the present invention may comprise from about 20 wt% to about 50 wt% of the electrode formulation of the invention and from about 50 wt% to about 80 wt% of a solvent or carrier liquid. For example, 100 kg of a slurry of the present invention may comprise from about 20 kg to about 50 kg electrode formulation and from about 50 kg to about 80 kg of a solvent or carrier liquid (e.g. the solvent or liquid carrier may present at the amount required to bring the total mass of the slurry to 100 kg). In certain embodiments, the slurry may consist essentially of the electrode formulation and a solvent or liquid carrier, for example, it may consist essentially of from about 20 wt% to about 50 wt% electrode formulation, and a solvent or liquid carrier to balance to 100%.

[0075] The slurry may have a viscosity of from about 5,000 mPa.s to about 10,000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C. For example, the slurry may have a viscosity of from about 6,000 mPa.s to about 9,000 mPa.s or from about 6,000 mPa.s to about 8,000 mPa.s when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C. In certain embodiments, the electrode formulation of the invention is a slurry with a viscosity of about 7,000 mPa.s when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C. A viscosity of about 7,000 mPa.s has been found to be especially effective for even coating of a support, such an aluminium foil, and provides an electrode that is robust, for example, an electrode that is less likely to fail during use due to short circuiting or the electrode formulation peeling away from the support.

[0076] The present inventors have found that when the electrode formulation comprises about 80 wt% of an active cathode material and about 1 wt% graphene, the formulation displays excellent conductivity, stability and / or capacity retention. Thus, in certain preferred embodiments, the electrode formulation of the present invention comprises about 1 wt% graphene. In certain exemplary embodiments, the electrode formulation comprises: a) about 80 wt% of a cathode active material; b) about 1 wt% graphene; c) about 1 wt% to about 20 wt% of a binder; and d) about 0 wt% to about 10 wt% of a carbon additive other than graphene or a graphene derivative; wherein the cathode active material and graphene form a composite material comprising particles of the cathode active material each coated with the graphene or graphene derivative.

[0077] For example, the electrode formulation of the present invention may comprise (or consist essentially of): a) about 80 wt% of a cathode active material (e.g. LiFePC ); b) about 1 wt% graphene; c) about 15 wt% of a binder (e.g. PVDF); and d) about 4 wt% of a carbon additive other than graphene or a graphene derivative (e.g. carbon black); wherein the cathode active material and graphene form a composite material comprising particles of the cathode active material each coated with the graphene or graphene derivative.

[0078] The present invention also provides a cathode electrode comprising a support coated with the electrode formulation of the present invention. The support may be any conductive material suitable for use in a cathode electrode. In certain embodiments, the support comprises aluminium, for example the support is an aluminium foil. The cathode electrode may have having a thickness of about 2 pm to about 20 pm, for example about 5 pm to about 7 pm.

[0079] Cathode electrodes comprising the electrode formulation of the present invention may be used in an electrochemical device, such as a battery. For example, the cathode electrode disclosed herein may be used in a lithium ion battery. In exemplary embodiments, the cathode electrode disclosed herein may be used in a pouch cell or coin cell (e.g. a lithium ion pouch cell or a lithium ion coin cell). When the battery is a pouch cell, the components of the battery may be contained within an aluminium laminated pouch casing.

[0080] A battery will typically comprise an anode electrode, a cathode electrode, a separator that is an ionically conductive membrane that separates the anode electrode and the cathode electrode, and an electrolyte. The selection of suitable materials and components for a battery is well understood by the person skilled in the art. The cathode electrode of the batteries disclosed herein comprise the electrode formulation of the present invention. The anode electrode may be composed of any suitable negative active material. For example, the negative active material may include a carbon-based material, a silicon- based material, a tin-based material, an antimony-based material, a lead-based material, a metal oxide (e.g. a lithium or sodium metal oxide). The carbon-based material may be, for example, soft carbon or hard carbon or a graphite-based material such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, or the like. Carbon nano-tube materials may be used. The silicon- based material may be, for example, silicon, a silicon oxide, a silicon-containing alloy, a mixture of the graphite-based material with the foregoing materials, or the like. The silicon oxide may be represented by SiOx(0< x <2). The silicon-containing alloy may be an alloy including silicon in the largest amount of the total metal elements (e.g., silicon being the metal element that is present in the largest amount of all the metal elements) based on the total amount of the alloy, for example, a Si-AI-Fe alloy. The tin-based material may be, for example, tin, a tin oxide, a tin-containing alloy, a mixture of the graphite-based material with the foregoing materials, or the like. Likewise for antimony and lead-based materials. The lithium metal oxide may be, for example, a titanium oxide compound such as Li4Ti50i2, Li2Ti60i3 or Li2Ti3O7. The sodium metal oxide may be, for example, a titanium oxide compound such as Na2Ti3O7or Na2Ti60i3. Other metal oxides that may be mentioned herein as suitable include, but are not limited to, TiO2, Fe2O3, Mo03. The anode in a sodium ion battery may be made a variety of materials including activated carbon, titanium phosphate, hard carbon or the like.

[0081] In exemplary embodiments, the battery is a lithium ion battery, and the anode comprises graphite, carboxymethylcellulose (CMC), and carbon additives (e.g. carbon black), for example it may comprise 80 wt% graphite, 15 wt% CMC, 5 wt% carbon additives (e.g. carbon black).

[0082] Suitable materials for a separator include, for example, a polyolefin-based resin, a polyester-based resin, polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene difluoride-hexafluoropropylene copolymer, a vinylidene difluoride- perfluorovinylether copolymer, a vinylidene difluoride-tetrafluoroethylene copolymer, a vinylidene difluoride-trifluoroethylene copolymer, a vinylidene difluoride-fluoroethylene copolymer, a vinylidene difluoride-hexafluoroacetone copolymer, a vinylidene difluorideethylene copolymer, a vinylidene difluoride-propylene copolymer, a vinylidene difluoridetrifluoropropylene copolymer, a vinylidene difluoride-tetrafluoroethylene- hexafluoropropylene copolymer, a vinylidene difluoride-ethylene-tetrafluoroethylene copolymer, and / or the like. The polyolefin-based resin may be polyethylene, polypropylene, and / or the like; and the polyester-based resin may be polyethylene terephthalate, polybutylene terephthalate, and / or the like. In exemplary embodiment, the separator is a PTFE membrane. Suitable membranes for use as a separator in a battery are commercially available.

[0083] The electrolyte is typically an organic solvent comprising an alkali metal salt (e.g. a lithium or sodium metal salt). For example, for a lithium ion battery the electrolyte may comprise LiPF6, LiBF4, and / or LiCIC in an organic solvent, such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, vinyl carbonate, or a mixture of two or more thereof. For a sodium ion battery the electrolyte may be NaCIC , NaPF6, or mixture thereof in a suitable organic solvent such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, and propylene carbonate. In exemplary embodiments, the battery is a lithium ion battery and the electrolyte is LiPF6in a mixture of ethylene carbonate, diethyl carbonate and vinyl carbonate (for example, at a 1 : 1 : 1 ratio).

[0084] The present invention also provides a method of preparing the electrode formulation of the present invention, and a method of preparing a cathode electrode using the electrode formulation of the present invention.

[0085] In certain embodiments, the method of preparing the electrode formulation of the present invention comprises the steps of: i. mixing a cathode active material with graphene or a graphene derivative to form a powder comprising the cathode active material and graphene; ii. dispersing the powder in a first solvent to form a colloidal solution; iii. removing the first solvent from the colloidal solution to provide a composite material comprising particles of the cathode active material, each particle partially or substantially coated with graphene or the graphene derivative; and iv. mixing the composite material with a binder to provide the electrode formulation.

[0086] Step i) may involve mixing the cathode active material with graphene or a graphene derivative and a carbon additive other than graphene or the graphene derivative to form the powder.

[0087] Step ii) may involve sonicating the powder in a first solvent to form the colloidal solution. For example, the powder and first solvent may be sonicated with a frequency of at least about 20 kHz to form the colloidal solution.

[0088] Step iii) may involve removing the first solvent by heating the colloidal solution and / or the first solvent may be removed under vacuum. Step iv) may involve mixing the composite material with a binder and a carbon additive other than graphene or graphene to provide the electrode formulation.

[0089] The method may optionally include a step of suspending the electrode formulation provided after step iv) in a second solvent to form a slurry. Preferably, the slurry has a viscosity of from about 5,000 to about 7,000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

[0090] The first solvent is preferably a polar protic solvent. For example, the first solvent may be water, methanol, ethanol, isopropyl alcohol, acetic acid, or mixture of two or more thereof. Typically, the first solvent is ethanol or acetone.

[0091] The second solvent is preferably an organic polar solvent, for example an aprotic polar solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, sulfolane, diphenyl sulfone, N-nethyl-2-pyrrolidone (NMP), or mixture of two or more thereof. Typically, the second solvent is NMP.

[0092] In certain other embodiments, the method of preparing the electrode formulation of the present invention comprises the steps of:

[0093] A. mixing a cathode active material with graphene or a graphene derivative, and optionally a carbon additive other the graphene or graphene to form a powder;

[0094] B. dispersing a binder in an organic solvent (e.g. NMP) to form a colloidal solution;

[0095] C. adding the powder from step A) into the colloidal solution of step B followed by mixing to disperse the powder in the organic solvent; and

[0096] D. optionally removing a portion or substantially all of the organic solvent from the colloidal solution in step C) to provide the electrode formulation. When a portion of the organic solvent is removed, the resulting electrode formulation is in the form of a slurry with a viscosity of from about 5,000 to about 7,000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

[0097] Also provided herein is a method of preparing a cathode electrode comprising the electrode formulation of the present invention. Such a method may comprise coating a support (e.g. an aluminium foil) with the electrode formulation of the present invention, followed by removing substantially all solvent that may be present in the electrode formulation (e.g. NMP). The cathode electrode typically having a thickness of about 2 pm to about 20 pm, for example about 5 pm to about 7 pm. The step of removing solvent from the electrode formulation may be achieved by heating the coated support at a temperature of about 50 °C to about 100 °C for about 1 hour to about 24 hours.

[0098] Also provided herein is a kit of parts suitable for preparing a cathode electrode of the present invention and / or assembling a battery comprising a cathode electrode of the present invention. The kit of parts may comprise:

[0099] - a cathode formulation of the present invention together with a suitable support (e.g. an aluminium foil), or cathode electrode of the present invention;

[0100] - an anode electrode;

[0101] - an electrolyte; and

[0102] - a separator.

[0103] It is within the skilled person abilities to select a suitable anode electrode, electrolyte and membrane separator to include in the kit of parts depending on the type of battery to be assembled. Examples of suitable anode electrode, electrolytes and separators are also provided herein.

[0104] The invention has been described broadly and generically herein. Those of ordinary skill in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present invention is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the scope of the present invention. Further, each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein. The following Examples illustrate the invention. that uses a cathode comprisina an electrode formulation of the present invention.

[0105] FIG. 1 is a flowchart of the preparation of a cathode electrode formulation and subsequent preparation of the cathode electrode according to the present example.

[0106] Step 1 : Preparation of cathode electrode formulation

[0107] About 8.5 kilogram LiFePC , 0.41 kilogram graphene, and 0.4 kilogram carbon black (Super P® Li) was loaded into a dry mixer (V Type Mixing System) and stirred at a speed of 300 to 400 rpm at normal pressure for approximately 8 hours. This was to ensure the dispersion of the solids and that there was no agglomeration. A powdered mixture was obtained.

[0108] 1 kilogram of PVDF and 16.48 kilograms of NMP were combined to obtain a colloidal solution. This colloidal solution was then placed in a planetary vacuum mixer and stirred at 60 to 1000 rpm for 5 to 10 minutes to ensure the initial dispersion of PVDF. The colloidal solution was then further stirred at increasing rotational speed of 3000 to 5000 rpm for approximately 30 minutes. The viscosity of the colloidal solution was approximately 5000 to 7000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1.5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C

[0109] The powdered mixture of LiFePC , graphene, and carbon black was added to the colloidal solution and further stirred at 1000 to 2000 rpm for another 30 minutes. The mixture was then vacuum evacuated down to a pressure of 0.060 MPa and stirred for another 8 hours. A water-cooling system was used to keep the temperature of the reactor at room temperature. The end product was in the form of a slurry with a viscosity of about 7000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1.5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

[0110] Step 2: Preparation of cathode electrode

[0111] The cathode slurry prepared from Step 1 was coated on an aluminium foil of 16-micron thickness. The coating process was performed by using a double layer extrusion coating machine with an optimized coating speed at 5m / min. After coating, the coated aluminium foil was dried at 80eC overnight. The final thickness of the cathode electrode was approximately 12 to 13 micron. The cathode electrode is referred to hereinafter as the LFP / G cathode. Table 1 provides further information of the LFP / G cathode.

[0112] Table 1 : Properties of the LFP / G Electrode

[0113] FIG. 2 shows a schematic diagram of the LFP / G cathode according to the present example.

[0114] Step 3: Assembling a battery comprising the cathode electrode

[0115] The battery prepared according to the present example is a pouch battery. FIG. 3 is a schematic diagram of the pouch battery, comprising a cathode, an anode and a separator.

[0116] A nonaqueous electrolytic solution comprising 1 M LiPF6in ethylene carbonate (EC), diethyl carbonate (DEC) and vinyl carbonate (VC) (the volume ratio of EC, DEC, VC was 1 : 1 : 1) was prepared.

[0117] An anode formulation comprising 80% graphite, 15% CMC and carbon black (Super P® Li) was prepared. The anode was prepared by combining 1.5 kilogram of carboxymethyl cellulose (CMC) and ~15 kilograms of water to obtain a colloidal solution. The colloidal solution was then placed in a planetary vacuum mixer and stirred at 60 to 1000 rpm for 5 to 10 minutes to ensure the initial dispersion of CMC. The colloidal solution was then further stirred at increasing rotational speed of 3000 to 5000 rpm for approximately 30 minutes. The viscosity of the colloidal solution was approximately 4000 to 5000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C. A powdered mixture of 8.0 kg graphite and 500 g of carbon black was added to the colloidal solution and further stirred at 1000 to 2000 rpm for another 30 minutes. The mixture was then vacuum evacuated down to a pressure of 0.060 MPa and stirred for another 8 hours. A water-cooling system was used to keep the temperature of the reactor at room temperature. The resulting slurry was coated onto a copper foil using a using double layers extrusion coating machine. The coated electrode was dried in an oven at a temperature of 80 °C.

[0118] A polytetrafluoroethylene (PTFE) separator was obtained from commercially available sources and used in the pouch battery to separate the cathode and anode.

[0119] The LFP / G cathode obtained from previous Step 2, the anode and the PTFE separator were cut into the desired size of the pouch battery. FIG. 4(b) is another schematic diagram showing the dimensions of the pouch battery. The cut LFP / G cathode, anode and PTFE separator were then stacked and placed into an aluminium laminated pouch casing. FIG. 4(a) includes photographs of the cut cathode, anode, PTFE separator and the aluminium laminated pouch casing. The nonaqueous electrolytic solution was then injected into the pouch battery casing at an amount of 3.8g / Ah. The pouch battery casing was sealed to obtain the pouch battery. FIG 4(c) is a photograph of the assembled pouch battery.

[0120] Results and Discussion

[0121] Cycle performance test of the battery

[0122] The battery was activated and underwent formation process for 3 cycles. The battery was charged using the constant current - constant voltage (CC-CV) method. Specifically, the battery was charged to 4.2V, with the 1 C constant-current charge, until it reaches the cut off voltage 4.2V, the charging method is switched to constant voltage mode at 4.2V until the current is decreased to 0.05C. Then the battery discharge at 1 C current charges down to 2.5V. After battery carries out 50 charge circulations, obtain circulation back discharge capacity 50 times. The battery capability retentions = 50 times circulation back discharge capacity / first.

[0123] The charge-discharge capacity curve of the 3.2V 10Ah LFP-G pouch cell during 100 cycles of cyclic charge-discharge in the potential range of 2.5V to 4.2V at 1 C current rate is shown in FIG. 5. The average discharge capacity was determined to be 10.49Ah, with a discharge energy per LFP-G cell unit of 32.95Wh. The LFP-G cell offers stable power delivery of 98% capacity retention upon 100 cycles. Table 2 provides a comparison in properties of the present LFP / G pouch battery compared to commercial LFP battery.

[0124] Table 2: Properties of LFP / G Pouch Cell Compared to Commercial LFP Battery

[0125] Field emission scanning electron microscopy (FE-SEM)

[0126] The microstructures of graphene in the LFP / G composite cathode were investigated by field emission scanning electron microscopy (FE-SEM). FIG. 6 are FE-SEM images showing the morphologies of the LFP / G composites and graphene. The shape of the LFP in the composite is more quasi-spherical with random size and aggregation and the graphene appears to cover most of the LFP particles (see FIG. 6(a) and FIG. 6(b)). While FIG. 6(c) showed the graphene image used in this work, it has a wrinkled, fluffy and disordered morphology. It is noted that the particle size distribution for the LFP / G particles is about 164.52 nm. A random aggregation phenomenon of the LFP particles was observed. Furthermore, it appears that the LFP particles are in contact with graphene to constitute a conducting network structure that can promote the electronic and ionic transport to improve the rate and cyclic performance of olivine-type LFP.

[0127] Raman spectroscopy

[0128] Raman spectroscopy provides information on the structural and vibrational modes of graphene and is used to determine the number of layers in graphene flakes. The most prominent spectral feature of carbon-based materials was the appearance of a D-band, G- band and a 2D-band at -1334, -1575 and -2676 cm"1respectively. The G-band corresponds to the graphitic structure and the 2D-band is a secondary peak that indicates the number of layers as it is highly sensitive to the layer stacking. With reference to FIG. 7 which is the Raman spectra of the graphene in the LFP / G composite electrode, the D-band for graphene were observed to be at 1345 cm-1and the G-band was observed at 1588 cm-1. The high degree of disordered graphene structure for graphene was confirmed with the appearance of G+D band, supporting the FE-SEM morphology images.

[0129] Optimizing the Graphene Concentration

[0130] FIG. 8 is a conductivity vs concentration of graphene in LFP / G cathode formulation graph. From the graph, the best conductivity is achieved with 1 % graphene in the cathode formulation with 105% improvement in conductivity compared to batteries using a LFP electrode formulation not containing graphene (conductivity of 1 .50 E-02 when no graphene present compared to 3.90E-02 when 1% graphene present).

[0131] Example 2 - Preparation of a further example of a pouch battery that uses a cathode comprising an electrode formulation of the present invention.

[0132] Step 1 : Preparation of cathode electrode formulation

[0133] LiFePO4, graphene, and carbon black (Super P® Li) were loaded into a dry mixer (V Type Mixing System) and stirred at a speed of 300 to 400 rpm at normal pressure for approximately 8 hours. This is to ensure the dispersion of the solids and that there was no agglomeration. A powdered mixture was obtained. The amounts of LiFePO4, graphene, and carbon black used were in line with those used in Example 1 .

[0134] 1 kilogram of PVDF and 16.48 kilograms of NMP were combined to obtain a colloidal solution. This colloidal solution was then placed in a planetary vacuum mixer and stirred at 60 to 1000 rpm for 5 to 10 minutes to ensure the initial dispersion of PVDF. The colloidal solution was then further stirred at increasing rotational speed of 3000 to 5000 rpm for approximately 30 minutes. The viscosity of the colloidal solution was approximately 5000 to 7000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1.5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

[0135] The powdered mixture of LiFePO4 with graphene and carbon black (Super P® Li) was loaded into a planetary vacuum mixer. The colloidal solution of PVDF and NMP was added into the planetary mixer in four stages for optimum mixing in order to obtain a homogeneous slurry. Specifically, the colloidal solution was injected into the planetary mixer four times with 1 hour in between injections during the mixing process. The total duration of the mixing process was about 12 hours such that the slurry obtained had a viscosity of about 5000- 7000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1.5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C. The mixing process was optimized at 800 to 1000 rpm for the main shaft and 400 rpm for the other shaft. The planetary mixer was also vacuumed down and filled with nitrogen gas and a water-cooling system was used to keep the temperature of the reactor below 60 °C.

[0136] Step 2: Preparation of cathode electrode

[0137] The cathode slurry prepared from previous Step 1 was coated on an aluminium foil of 16 micron thickness. The coating process was performed by using a double layer extrusion coating machine with an optimized coating speed at 5m / min. After coating, the coated aluminium foil was dried at 80 °C overnight. The final thickness of the cathode electrode was approximately 5 pm to 7 pm.

[0138] Step 3: Assembling a battery comprising the cathode electrode

[0139] The cathode electrode prepared from the Step 2 was assembled into a pouch battery by following Step 3 of Example 1 . Polypropylene was used as the separator for the pouch battery.

[0140] Example 3 - Preparation of a coin cell that uses a cathode comprising an electrode formulation of the present invention.

[0141] FIG. 9 is a flowchart of the preparation of a cathode electrode formulation and subsequent preparation of the cathode electrode according to the present example.

[0142] Step 1 : Preparation of cathode electrode formulation

[0143] LiFePC with graphene were mixed using a mortar to produce a fine powder mixture of LiFePC and graphene (referred to herein after as the LFP / G mixture). The LFP / G mixture was then added into the ethanol solution to produce a suspended colloidal solution.

[0144] The colloidal solution was then ultra-sonicated using an ultrasonic dispersion machine. The sonication process was performed using a pulse interval 5 second sonication followed by 3 second rest. The process was repeated for 1 hour.

[0145] The colloidal solution of the LFP / G mixture was allowed to rest for 30 minutes after the sonication process. Then the colloidal solution was further filtered, and the LFP / G mixture was collected and dried at 80 °C overnight. The final product was a finely dispersed LFP / G powder. Carbon black (Super P® Li) and PVDF were added into the LFP / G powder inside a mortar and softly ground until well mixed, thus provide an electrode formulation containing 80 wt% LFP, 1 wt% Graphene, 15 wt% PVDF and 4 wt% carbon black (Super P® Li).

[0146] NMP was slowly added to the electrode formulation to produce a homogenous slurry. The end slurry contained about 73 wt% NMP. The slow addition of NMP was required to ensure no agglomeration of the electrode formulation in the slurry, which would affect the battery performance.

[0147] Step 2: Preparation of cathode electrode

[0148] The cathode slurry from Step 1 was coated on an aluminium foil of 16 micron thickness. The coating process was performed using an automated doctor blade coating machine, with an optimized coating speed of 5 mm / sec. After coating, the coated aluminium foil was dried at 80 °C overnight. The final thickness of the cathode electrode was approximate 5 to 7 micron.

[0149] Step 3: Assemblino of coin cell comorisino the cathode electrode

[0150] A nonaqueous electrolytic solution comprising 1 M LiPF6in ethylene carbonate (EC), diethyl carbonate (DEC) and vinyl carbonate (VC) (the volume ratio of EC, DEC, VC is 1 : 1 : 1 ) was prepared.

[0151] Commercially purchased battery grade lithium disc was used as the anode.

[0152] The cathode obtained from Step 2 was cut into a circular shape with the diameter 20mm. A propylene separator was used to separate the cathode and anode. The cathode, anode and propylene separator were stacked and assembled into a coin cell. Then nonaqueous electrolytic solution was injected into the coin cell at the amount of 3.8g / Ah.

[0153] Results and Discussion

[0154] Cycle performance test

[0155] The battery was activated and underwent formation process for 3 cycles. The battery was charged using the constant current - constant voltage (CC-CV) method. Specifically, the battery was charged to 4.2V, with the 0.5C constant-current charge, until it reaches the cut off voltage 4.2V, the charging method is switched to constant voltage mode at 4.2V until the current is decreased to 0.05C. Then the battery discharge at 0.5C current charges down to 2.5V. After battery carries out 50 charge circulations, obtain circulation back discharge capacity 50 times. The battery capability retentions = 50 times circulation back discharge capacity / first.

[0156] The charging / discharging voltage profile for the coin cell using the LFP / G cathode showed a notable difference compared with a coin cell using a cathode loaded with only LFP. The voltage profiles of the cyclic performance showed the potential differences between the voltage plateaus of charge and discharge profiles of LFP / G cathode is smaller than the LFP only cathode. The larger gap between the charge and discharge plateaus may be caused by the inferior conductivity of the electrode material. As compared with LFP electrodes, the polarizations of the LFP / G electrodes upon cycling are smaller, benefiting from the superior electrical conductivity by the addition of graphene to LFP.

Claims

Claims1 . An electrode formulation comprising: a) about 70 wt% to about 90 wt% of a cathode active material; b) about 0.1 wt% to about 5 wt% graphene; c) about 1 wt% to about 20 wt% of a binder; and d) about 0 wt% to about 10 wt% of a carbon additive other than graphene or a graphene derivative; wherein the cathode active material and graphene are present in the form of a composite material comprising particles of the cathode active material each partially or substantially coated with graphene.

2. The electrode formulation of claim 1 , wherein the cathode active material is selected from the group consisting of LixFePC , LixNiCOMnO2, LixCo02, LixNiO0.33Co0.33AI0.33O2, LixMn2O4, and LixNio.5Mn1.5O4, for example the cathode active material may be LiFePO4.

3. The electrode formulation of claim 1 , wherein the binder is polyvinylidene fluoride (PVDF).

4. The electrode formulation of claim 1 comprising about 75 wt% to about 85 wt% of the cathode active material, for example about 80 wt% of the cathode active material.

5. The electrode formulation of claim 1 comprising about 0.5 wt% to about 2 wt% graphene, for example about 1 wt% graphene.

6. The electrode formulation of claim 1 comprising about 5 wt% to about 20 wt% of the binder, for example about 15 wt% of the binder.

7. The electrode formulation of claim 1 comprising about 0 wt% to about 5 wt% of a carbon additive other than graphene or a graphene derivative, for example about 4 wt%.

8. The electrode formulation of claim 1 , wherein the carbon additive other than graphene or a graphene derivative is carbon black.

9. The electrode formulation of claim 1 comprising about 75 wt% to about 95 wt% of the composite material.

10. The electrode formulation of claim 1 , wherein the cathode active material and graphene are present in the composite material at a weight ratio of about 70:1 to about 90:1 , for example about 80:1 .

11. A slurry comprising the electrode formulation of claim 1 and an organic solvent.

12. The slurry of claim 1 1 , wherein the slurry has a viscosity of about 5,000 mPa.s to about 7,000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1.5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

13. The slurry of claim 1 1 , wherein the organic solvent is N-methyl-2-pyrrolidone (NMP).

14. A cathode electrode comprising a support coated with the electrode formulation of claim 1 or the slurry of claim 11 .

15. The cathode electrode of claim 14, wherein the support comprises aluminium, for example the support is an aluminium foil.

16. The cathode electrode of claim 14 having a thickness of about 2 pm to about 20 pm, for example about 5 pm to about 7 pm.

17. A battery comprising the cathode electrode of claim 14.

18. The battery of claim 17, wherein the battery is a lithium ion battery, for example a lithium ion full cell battery.

19. The battery of claim 17, wherein the battery is a pouch cell.

20. A kit of parts comprising: a cathode formulation according to claim 1 , or the slurry of claim 1 1 , together with a support (e.g. an aluminium foil); or cathode electrode according to claim 14; an anode electrode; an electrolyte; and a separator.

21. A method of preparing the electrode formulation of claim 1 , wherein the method comprises: i. mixing a cathode active material with graphene or a graphene derivative to form a powder comprising the cathode active material and graphene; ii. dispersing the powder in a first solvent to form a colloidal solution; iii. removing the first solvent from the colloidal solution to provide a composite material comprising particles of the cathode active material each coated with graphene or the graphene derivative; and iv. mixing the composite material with a binder to provide the electrode formulation.

22. The method according to claim 21 , wherein step i) comprises mixing the cathode active material with graphene or a graphene derivative and a carbon additive other than graphene or the graphene derivative to form the powder.

23. The method according to claim 21 , wherein step iv) comprises mixing the composite material with a binder and a carbon additive other the graphene or graphene.

24. The method according to claim 21 , wherein step ii) comprises sonicating the colloidal solution.

25. The method according to claim 21 , wherein the colloidal solution is sonicated at a frequency of at least 20 kHz.

26. The method according to claim 21 , wherein the first solvent is a polar protic solvent, for example ethanol.

27. The method according to claim 21 , wherein the method further comprises a step of suspending the electrode formulation provided after step iv) in a second solvent to form a slurry.

28. The method according to claim 27, wherein the slurry has a viscosity of about 5,000 to about 7,000 mPa.s, when measured using a rotation viscometer with a rotation rate of 1 .5 rpm (equivalent to a shear rate of 5.1 s-1) at a temperature of 25 °C.

29. The method according to claim 27, wherein the second solvent is NMP.

30. A method of preparing a cathode electrode, the method comprising coating a support with the slurry of claim 11 , followed by removing substantially all of the organic solvent from the slurry to provide the cathode electrode.

31. The method according to claim 30, wherein the support is coated with the slurry followed by heating the support at a temperature of about 50 °C to about 100 °C for about 1 hour to about 24 hours.

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